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ASD/LRFD

NDS

National Design Specification

for Wood Construction

2012 EDITIONUpdates and ErrataWhile every precaution has been taken toensure the accuracy of this document, errorsmay have occurred during development.Updates or Errata are posted to the AmericanWood Council website at www.awc.org.Technical inquiries may be addressed toinfo@awc.org.

The American Wood Council (AWC) is the voice of North American traditional and engineered woodproducts. From a renewable resource that absorbs and sequesters carbon, the wood products industrymakes products that are essential to everyday life. AWCs engineers, technologists, scientists, andbuilding code experts develop state-of-the-art engineering data, technology, and standards on structuralwood products for use by design professionals, building officials, and wood products manufacturers toassure the safe and efficient design and use of wood structural components. ANSI/AWC NDS-2012 Approval Date: August 15, 2011

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ISBN 978-0-9827380-7-8ISBN 978-0-9827380-6-1 (4 Volume Set)

Copyright 2012 by American Wood Council

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FOREWORD The National Design Specification for Wood construction. Particular attention is directed to Sec-Construction (NDS) was first issued by the Na- tion 2.1.2, relating to the designers responsibility totional Lumber Manufacturers Association (now the make adjustments for particular end uses of structures.American Wood Council) (AWC) in 1944, under the Since the first edition of the NDS in 1944, thetitle National Design Specification for Stress-Grade Associations Technical Advisory Committee hasLumber and Its Fastenings. By 1971, the scope of continued to study and evaluate new data and devel-the Specification had broadened to include additional opments in wood design. Subsequent editions of thewood products. In 1977, the title was changed to Specification have included appropriate revisions toreflect the new nature of the Specification, and the provide for use of such new information. This edi-content was rearranged to simplify its use. The 1991 tion incorporates numerous changes considered byedition was reorganized in an easier to use equation AWCs ANSI-accredited Wood Design Standardsformat, and many sections were rewritten to provide Committee. The contributions of members of thisgreater clarity. Committee to improvement of the Specification as a In 1992, the American Forest & Paper Association national design standard for wood construction are(AF&PA) formerly the National Forest Products especially recognized.Association was accredited as a canvass sponsor by Acknowledgement is also made to the Forestthe American National Standards Institute (ANSI). Products Laboratory, U.S. Department of Agriculture,The Specification subsequently gained approval as for data and publications generously made avail-an American National Standard designated ANSI/ able, and to the engineers, scientists, and other usersNFoPA NDS-1991 with an approval date of October who have suggested changes in the content of the16, 1992. Specification. AWC invites and welcomes comments, In 2010, AWC was separately incorporated, re- inquiries, suggestions, and new data relative to thechartered, and accredited by ANSI as a standards provisions of this document.developing organization. The current edition of the It is intended that this document be used in con-Standard is designated ANSI/AWC NDS-2012 with junction with competent engineering design, accuratean approval date of August 15, 2011. fabrication, and adequate supervision of construction. In developing the provisions of this Specification, AWC does not assume any responsibility for errorsthe most reliable data available from laboratory tests or omissions in the document, nor for engineeringand experience with structures in service have been designs, plans, or construction prepared from it.carefully analyzed and evaluated for the purpose of Those using this standard assume all liability aris-providing, in convenient form, a national standard ing from its use. The design of engineered structuresof practice. is within the scope of expertise of licensed engineers, It is intended that this Specification be used in architects, or other licensed professionals for applica-conjunction with competent engineering design, tions to a particular structure.accurate fabrication, and adequate supervision of American Wood Council

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Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION LIST OF TABLES FOR WOOD CONSTRUCTION vii

Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL2 GENERAL REQUIREMENTS FOR STRUCTURAL DESIGN

1.1 Scope1.1.1 Practice Defined 53 for design provisions for commonly used panel products). 1.1.1.1 This Specification defines the method to be 1.1.1.3 Structural assemblies utilizing metal con-followed in structural design with the following wood nector plates shall be designed in accordance with ac-products: cepted engineering practice (see Reference 9). - visually graded lumber 1.1.1.4 This Specification is not intended to pre- - mechanically graded lumber clude the use of materials, assemblies, structures or de- - structural glued laminated timber signs not meeting the criteria herein, where it is demon- - timber piles strated by analysis based on recognized theory, full- - timber poles scale or prototype loading tests, studies of model ana- - prefabricated wood I-joists logues or extensive experience in use that the material, - structural composite lumber assembly, structure or design will perform satisfactorily - wood structural panels in its intended end use.It also defines the practice to be followed in the designand fabrication of single and multiple fastener connec- 1.1.2 Competent Supervisiontions using the fasteners described herein. 1.1.1.2 Structural assemblies utilizing panel prod- The reference design values, design value adjust-ucts shall be designed in accordance with principles of ments, and structural design provisions in this Specifi-engineering mechanics (see References 32, 33, 34, and cation are for designs made and carried out under com- petent supervision.

1.2 General Requirements

1.2.1 Conformance with Standards 1.2.2 Framing and Bracing

The quality of wood products and fasteners, and the All members shall be so framed, anchored, tied, anddesign of load-supporting members and connections, braced that they have the required strength and rigidity.shall conform to the standards specified herein. Adequate bracing and bridging to resist wind and other lateral forces shall be provided.

1.3 Standard as a Whole

The various Chapters, Sections, Subsections and of each Chapter, Section, Subsection, and Article shallArticles of this Specification are interdependent and, apply to every other Chapter, Section, Subsection, andexcept as otherwise provided, the pertinent provisions Article.

1.4 Design Procedures

This Specification provides requirements for the 1.4.1 Loading Assumptionsdesign of wood products specified herein by the follow-ing methods: Wood buildings or other wood structures, and their (a) Allowable Stress Design (ASD) structural members, shall be designed and constructed (b) Load and Resistance Factor Design (LRFD) to safely support all anticipated loads. This Specifica- Designs shall be made according to the provisions tion is predicated on the principle that the loading as-for Allowable Stress Design (ASD) or Load and Resis- sumed in the design represents actual conditions.tance Factor Design (LRFD). Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 3

1.4.2 Governed by Codes 1.4.4 Load Combinations

1 Minimum design loads shall be in accordance with Combinations of design loads and forces, and loadthe building code under which the structure is designed, combination factors, shall be in accordance with theor where applicable, other recognized minimum design building code under which the structure is designed, or

GENERAL REQUIREMENTS FOR STRUCTURAL DESIGN

load standards. where applicable, other recognized minimum design load standards (see Reference 5 for additional informa-1.4.3 Loads Included tion). The governing building code shall be permitted to be consulted for load combination factors. Load combi- Design loads include any or all of the following nations and associated time effect factors, , for use inloads or forces: dead, live, snow, wind, earthquake, LRFD are provided in Appendix N.erection, and other static and dynamic forces.

1.5 Specifications and Plans

1.5.1 Sizes

The plans or specifications, or both, shall indicate

whether wood products sizes are stated in terms of stan-dard nominal, standard net or special sizes, as specifiedfor the respective wood products in Chapters 4, 5, 6, 7,8, and 9.

1.6 Notation Except where otherwise noted, the symbols used in CP = column stability factorthis Specification have the following meanings: CT = buckling stiffness factor for dimension lumber A = area of cross section, in. 2

CV = volume factor for structural glued laminated

Acritical = minimum shear area for any fastener in a row, timber or structural composite lumber in. 2

Cb = bearing area factor

Agroup-net = critical group net section area between first Cc = curvature factor for structural glued laminated and last row of fasteners, in. 2

3 = distance from center of spacer block to cen- = angle between the wood surface and the direc- troid of group of split ring or shear plate con- tion of applied load for dowel-type fasteners nectors in end block for a spaced column, in. subjected to combined lateral and withdrawal loading, degrees m.c. = moisture content based on oven-dry weight of wood, % eff = effective char rate (in./hr.) adjusted for expo- sure time, t n = number of fasteners in a row n = nominal char rate (in./hr.), linear char rate based nR = number of rivet rows on 1-hour exposure nc = number of rivets per row = load/slip modulus for a connection, lbs/in. ni = number of fasteners in a row = time effect factor nrow = number of rows of fasteners

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Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL10 DESIGN VALUES FOR STRUCTURAL MEMBERS

2.1 General2.1.1 General Requirement 2.1.2 Responsibility of Designer to Adjust for Conditions of Use Each wood structural member or connection shallbe of sufficient size and capacity to carry the applied Adjusted design values for wood members and con-loads without exceeding the adjusted design values nections in particular end uses shall be appropriate forspecified herein. the conditions under which the wood is used, taking into 2.1.1.1 For ASD, calculation of adjusted design val- account the differences in wood strength properties withues shall be determined using applicable ASD adjust- different moisture contents, load durations, and types ofment factors specified herein. treatment. Common end use conditions are addressed in 2.1.1.2 For LRFD, calculation of adjusted design this Specification. It shall be the final responsibility ofvalues shall be determined using applicable LRFD ad- the designer to relate design assumptions and referencejustment factors specified herein. design values, and to make design value adjustments appropriate to the end use.

2.3 Adjustment of Reference Design Values

2.3.1 Applicability of Adjustment sign load for a cumulative duration of approximately ten years. When the cumulative duration of the full maxi-Factors mum load does not exceed the specified time period, all reference design values except modulus of elasticity, E, Reference design values shall be multiplied by all modulus of elasticity for beam and column stability,applicable adjustment factors to determine adjusted de- Emin, and compression perpendicular to grain, Fc, basedsign values. The applicability of adjustment factors to on a deformation limit (see 4.2.6) shall be multiplied bysawn lumber, structural glued laminated timber, poles the appropriate load duration factor, CD, from Tableand piles, prefabricated wood I-joists, structural com- 2.3.2 or Figure B1 (see Appendix B) to take into ac-posite lumber, wood structural panels, and connection count the change in strength of wood with changes indesign values is defined in 4.3, 5.3, 6.3, 7.3, 8.3, 9.3, load duration.and 10.3, respectively. 2.3.2.2 The load duration factor, CD, for the shortest duration load in a combination of loads shall apply for2.3.2 Load Duration Factor, CD (ASD that load combination. All applicable load combinationsOnly) shall be evaluated to determine the critical load combi- nation. Design of structural members and connections 2.3.2.1 Wood has the property of carrying substan- shall be based on the critical load combination (see Ap-tially greater maximum loads for short durations than pendix B.2).for long durations of loading. Reference design values 2.3.2.3 The load duration factors, CD, in Table 2.3.2apply to normal load duration. Normal load duration and Appendix B are independent of load combinationrepresents a load that fully stresses a member to its al- factors, and both shall be permitted to be used in designlowable design value by the application of the full de- calculations (see 1.4.4 and Appendix B.4). Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 11

3.1 General3.1.1 Scope connectors shall be considered as occurring at the same critical section if the parallel to grain spacing between Chapter 3 establishes general design provisions that connectors in adjacent rows is less than or equal to oneapply to all wood structural members and connections connector diameter (see Figure 3A).covered under this Specification. Each wood structuralmember or connection shall be of sufficient size and Figure 3B Net Cross Section at acapacity to carry the applied loads without exceeding Split Ring or Shear Platethe adjusted design values specified herein. Reference Connectiondesign values and specific design provisions applicableto particular wood products or connections are given inother Chapters of this Specification.

3.1.2 Net Section Area

3.1.2.1 The net section area is obtained by deduct-

ing from the gross section area the projected area of allmaterial removed by boring, grooving, dapping, notch-ing, or other means. The net section area shall be usedin calculating the load carrying capacity of a member,except as specified in 3.6.3 for columns. The effects ofany eccentricity of loads applied to the member at thecritical net section shall be taken into account. 3.1.3 Connections 3.1.2.2 For parallel to grain loading with staggeredbolts, drift bolts, drift pins, or lag screws, adjacent fas- Structural members and fasteners shall be arrangedteners shall be considered as occurring at the same symmetrically at connections, unless the bending mo-critical section if the parallel to grain spacing between ment induced by an unsymmetrical arrangement (suchfasteners in adjacent rows is less than four fastener di- as lapped joints) has been accounted for in the design.ameters (see Figure 3A). Connections shall be designed and fabricated to insure that each individual member carries its proportionalFigure 3A Spacing of Staggered stress. Fasteners 3.1.4 Time Dependent Deformations

Where members of structural frames are composed

of two or more layers or sections, the effect of time de- pendent deformations shall be accounted for in the de- sign (see 3.5.2 and Appendix F).

3.1.5 Composite Construction

Composite constructions, such as wood-concrete,

3.1.2.3 The net section area at a split ring or shear wood-steel, and wood-wood composites, shall be de-plate connection shall be determined by deducting from signed in accordance with principles of engineeringthe gross section area the projected areas of the bolt mechanics using the adjusted design values for struc-hole and the split ring or shear plate groove within the tural members and connections specified herein.member (see Figure 3B and Appendix K). Where splitring or shear plate connectors are staggered, adjacent Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 15

3.2 Bending Members General

3.2.1 Span of Bending Members 3.2.3 Notches

For simple, continuous and cantilevered bending 3.2.3.1 Bending members shall not be notched ex-members, the span shall be taken as the distance from cept as permitted by 4.4.3, 5.4.5, 7.4.4, and 8.4.1. Aface to face of supports, plus the required bearinglength at each end. gradual taper cut from the reduced depth of the member to the full depth of the member in lieu of a square- 3 cornered notch reduces stress concentrations.3.2.2 Lateral Distribution of 3.2.3.2 The stiffness of a bending member, as de-

DESIGN PROVISIONS AND EQUATIONS

termined from its cross section, is practically unaffectedConcentrated Load by a notch with the following dimensions: notch depth (1/6) (beam depth) Lateral distribution of concentrated loads from a notch length (1/3) (beam depth)critically loaded bending member to adjacent parallel 3.2.3.3 See 3.4.3 for effect of notches on shearbending members by flooring or other cross members strength.shall be permitted to be calculated when determiningdesign bending moment and vertical shear force (see15.1).

3.3 Bending Members Flexure

3.3.1 Strength in Bending 3.3.3 Beam Stability Factor, CL

The actual bending stress or moment shall not ex- 3.3.3.1 When the depth of a bending member doesceed the adjusted bending design value. not exceed its breadth, d b, no lateral support is re- quired and CL = 1.0.3.3.2 Flexural Design Equations 3.3.3.2 When rectangular sawn lumber bending members are laterally supported in accordance with 3.3.2.1 The actual bending stress induced by a 4.4.1, CL = 1.0.bending moment, M, is calculated as follows: 3.3.3.3 When the compression edge of a bending member is supported throughout its length to prevent Mc M (3.3-1) lateral displacement, and the ends at points of bearing fb

I S have lateral support to prevent rotation, CL = 1.0. For a rectangular bending member of breadth, b, 3.3.3.4 Where the depth of a bending member ex-and depth, d, this becomes: ceeds its breadth, d > b, lateral support shall be pro- vided at points of bearing to prevent rotation. When M 6M (3.3-2) such lateral support is provided at points of bearing, but f b S bd2 no additional lateral support is provided throughout the length of the bending member, the unsupported length, 3.3.2.2 For solid rectangular bending members with u, is the distance between such points of end bearing,the neutral axis perpendicular to depth at center: or the length of a cantilever. When a bending member bd3 (3.3-3) is provided with lateral support to prevent rotation at I moment of inertia, in.4 12 intermediate points as well as at the ends, the unsup- ported length, u, is the distance between such points of I bd2 (3.3-4) S section modulus, in.3 intermediate lateral support. c 6 3.3.3.5 The effective span length, e, for single span or cantilever bending members shall be determined in accordance with Table 3.3.3.

DESIGN PROVISIONS AND EQUATIONS

CL (3.3-6) dix F for information concerning coefficient of varia- 1.9 1.9 0.95 tion in modulus of elasticity (COVE). 3.3.3.10 Members subjected to flexure about both principal axes (biaxial bending) shall be designed in accordance with 3.9.2.

3.4 Bending Members Shear

3.4.1 Strength in Shear Parallel to 3.4.3 Shear DesignGrain (Horizontal Shear) 3.4.3.1 When calculating the shear force, V, in 3.4.1.1 The actual shear stress parallel to grain or bending members:shear force at any cross section of the bending member (a) For beams supported by full bearing on oneshall not exceed the adjusted shear design value. A surface and loads applied to the opposite sur-check of the strength of wood bending members in face, uniformly distributed loads within a dis-shear perpendicular to grain is not required. tance from supports equal to the depth of the 3.4.1.2 The shear design procedures specified bending member, d, shall be permitted to be ig-herein for calculating fv at or near points of vertical nored. For beams supported by full bearing onsupport are limited to solid flexural members such as one surface and loads applied to the oppositesawn lumber, structural glued laminated timber, struc- surface, concentrated loads within a distance, d,tural composite lumber, or mechanically laminated tim- from supports shall be permitted to be multi-ber beams. Shear design at supports for built-up com- plied by x/d where x is the distance from theponents containing load-bearing connections at or near beam support face to the load (see Figure 3C).points of support, such as between the web and chord ofa truss, shall be based on test or other techniques. Figure 3C Shear at Supports

(b) The largest single moving load shall be placed stress parallel to grain nearly to that computed at a distance from the support equal to the for an unnotched bending member with a depth depth of the bending member, keeping other of dn. loads in their normal relation and neglecting (e) When a bending member is notched on the any load within a distance from a support equal compression face at the end as shown in Figure to the depth of the bending member. This con- 3D, the adjusted design shear, Vr', shall be cal- dition shall be checked at each support. culated as follows: (c) With two or more moving loads of about equal weight and in proximity, loads shall be placed 2 d dn Vr Fv b d e (3.4-5) in the position that produces the highest shear 3 dn force, V, neglecting any load within a distance where: from a support equal to the depth of the bend- ing member. e = the distance the notch extends from the 3.4.3.2 For notched bending members, shear force, inner edge of the support and must be lessV, shall be determined by principles of engineering me- than or equal to the depth remaining at thechanics (except those given in 3.4.3.1). notch, e dn. If e > dn, dn shall be used to cal- (a) For bending members with rectangular cross culate fv using Equation 3.4-2, in. section and notched on the tension face (see 3.2.3), the adjusted design shear, Vr', shall be dn = depth of member remaining at a notch calculated as follows: meeting the provisions of 3.2.3, measured 2 perpendicular to length of member. If the 2 d Vr Fvbdn n (3.4-3) end of the beam is beveled, as shown by 3 d the dashed line in Figure 3D, dn is measuredwhere: from the inner edge of the support, in.

d = depth of unnotched bending member, in.

Figure 3D Bending Member End- dn = depth of member remaining at a notch Notched on Compression measured perpendicular to length of mem- ber, in. Face

Fv' = adjusted shear design value parallel to

grain, psi

(b) For bending members with circular cross sec-

tion and notched on the tension face (see 3.2.3), the adjusted design shear, Vr', shall be calcu- lated as follows: 2 2 d Vr Fv An n (3.4-4) 3 d 3.4.3.3 When connections in bending members are fastened with split ring connectors, shear plate connec-where: tors, bolts, or lag screws (including beams supported by An = cross-sectional area of notched member, such fasteners or other cases as shown in Figures 3E in2 and 3I) the shear force, V, shall be determined by prin- ciples of engineering mechanics (except those given in 3.4.3.1). (c) For bending members with other than rectangu- (a) Where the connection is less than five times the lar or circular cross section and notched on the depth, 5d, of the member from its end, the ad- tension face (see 3.2.3), the adjusted design justed design shear, Vr', shall be calculated as shear, Vr', shall be based on conventional engi- follows: neering analysis of stress concentrations at notches. 2 d 2

(d) A gradual change in cross section compared Vr Fvbde e (3.4-6)

3 d with a square notch decreases the actual shear Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 19

where: (b) Where the connection is at least five times the

depth, 5d, of the member from its end, the ad- for split ring or shear plate connections: justed design shear, Vr', shall be calculated as de = depth of member, less the distance from follows: the unloaded edge of the member to the 2 nearest edge of the nearest split ring or Vr Fv bde (3.4-7) 3 shear plate connector (see Figure 3E), in.

for bolt or lag screw connections:

(c) Where concealed hangers are used, the adjusted design shear, Vr', shall be calculated based on 3 de = depth of member, less the distance from the provisions in 3.4.3.2 for notched bending the unloaded edge of the member to the members.

3.5.2 Long-Term Loading joists, or structural composite lumber used

in dry service conditions as defined in 4.1.4, Where total deflection under long-term loading 5.1.4, 7.1.4, and 8.1.4, respectively.must be limited, increasing member size is one way to Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL20 DESIGN PROVISIONS AND EQUATIONS

= 2.0 for structural glued laminated timber = 2.0 for unseasoned lumber or for seasoned used in wet service conditions as defined in lumber used in wet service conditions as 5.1.4. defined in 4.1.4.

= 2.0 for wood structural panels used in dry LT = immediate deflection due to the long-term service conditions as defined in 9.1.4. component of the design load, in.

ST = deflection due to the short-term or normal

component of the design load, in.

3.6 Compression Members General

3.6.1 Terminology compression design value parallel to grain multiplied by all applicable adjustment factors except the column For purposes of this Specification, the term col- stability factor, CP.umn refers to all types of compression members, in-cluding members forming part of trusses or other struc- Figure 3F Simple Solid Columntural components.

3.6.2 Column Classifications

3.6.2.1 Simple Solid Wood Columns. Simple col-

umns consist of a single piece or of pieces properlyglued together to form a single member (see Figure 3F). 3.6.2.2 Spaced Columns, Connector Joined. Spacedcolumns are formed of two or more individual memberswith their longitudinal axes parallel, separated at theends and middle points of their length by blocking andjoined at the ends by split ring or shear plate connectorscapable of developing the required shear resistance (see15.2). 3.6.2.3 Built-Up Columns. Individual laminationsof mechanically laminated built-up columns shall bedesigned in accordance with 3.6.3 and 3.7, except thatnailed or bolted built-up columns shall be designed inaccordance with 15.3.

3.6.3 Strength in Compression

3.6.4 Compression MembersParallel to Grain Bearing End to End The actual compression stress or force parallel tograin shall not exceed the adjusted compression design For end grain bearing of wood on wood, and onvalue. Calculations of fc shall be based on the net sec- metal plates or strips see 3.10.tion area (see 3.1.2) where the reduced section occurs inthe critical part of the column length that is most sub- 3.6.5 Eccentric Loading orject to potential buckling. Where the reduced section Combined Stressesdoes not occur in the critical part of the column lengththat is most subject to potential buckling, calculations For compression members subject to eccentricof fc shall be based on gross section area. In addition, fc loading or combined flexure and axial loading, see 3.9based on net section area shall not exceed the reference and 15.4. Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 21

DESIGN PROVISIONS AND EQUATIONS

3.7.1 Column Stability Factor, CP 3.7.1.6 For especially severe service conditions and/or extraordinary hazard, use of lower adjusted de- 3.7.1.1 When a compression member is supported sign values may be necessary. See Appendix H forthroughout its length to prevent lateral displacement in background information concerning column stabilityall directions, CP = 1.0. calculations and Appendix F for information concern- 3.7.1.2 The effective column length, e, for a solid ing coefficient of variation in modulus of elasticitycolumn shall be determined in accordance with princi- (COVE).ples of engineering mechanics. One method for deter-mining effective column length, when end-fixity condi- 3.7.2 Tapered Columnstions are known, is to multiply actual column length bythe appropriate effective length factor specified in Ap- For design of a column with rectangular cross sec-pendix G, e = (Ke)(). tion, tapered at one or both ends, the representative di- 3.7.1.3 For solid columns with rectangular cross mension, d, for each face of the column shall be derivedsection, the slenderness ratio, e/d, shall be taken as the as follows:larger of the ratios e1/d1 or e2/d2 (see Figure 3F) where d each ratio has been adjusted by the appropriate buck- d dmin (dmax dmin ) a 0.15 1 min (3.7-2)ling length coefficient, Ke, from Appendix G. dmax 3.7.1.4 The slenderness ratio for solid columns, where:e/d, shall not exceed 50, except that during construc-tion e/d shall not exceed 75. d = representative dimension for tapered 3.7.1.5 The column stability factor shall be calcu- column, in.lated as follows: dmin = the minimum dimension for that face of the

Calculations of fc and CP shall be based on the rep- 3.7.3 Round Columns

resentative dimension, d. In addition, fc at any crosssection in the tapered column shall not exceed the ref- The design of a column of round cross section shallerence compression design value parallel to grain mul- be based on the design calculations for a square columntiplied by all applicable adjustment factors except the of the same cross-sectional area and having the samecolumn stability factor, CP. degree of taper. Reference design values and special design provisions for round timber poles and piles are provided in Chapter 6.

3.8 Tension Members

3.8.1 Tension Parallel to Grain 3.8.2 Tension Perpendicular to Grain The actual tension stress or force parallel to grainshall be based on the net section area (see 3.1.2) and Designs that induce tension stress perpendicular toshall not exceed the adjusted tension design value. grain shall be avoided whenever possible (see Refer- ences 16 and 19). When tension stress perpendicular to grain cannot be avoided, mechanical reinforcement suf- ficient to resist all such stresses shall be considered (see References 52 and 53 for additional information).

fb1 = actual edgewise bending stress (bending

fb2 = actual flatwise bending stress (bending

load applied to wide face of member) , psi

d1 = wide face dimension (see Figure 3H), in.

d2 = narrow face dimension (see Figure 3H), in.

3.10 Design for Bearing

3.10.1 Bearing Parallel to Grain it shall be equivalent to 20-gage metal plate or better, inserted with a snug fit between abutting ends. 3.10.1.1 The actual compressive bearing stress par-allel to grain shall be based on the net bearing area and 3.10.2 Bearing Perpendicular toshall not exceed the reference compression design value Grainparallel to grain multiplied by all applicable adjustmentfactors except the column stability factor, CP. The actual compression stress perpendicular to 3.10.1.2 Fc*, the reference compression design val- grain shall be based on the net bearing area and shallues parallel to grain multiplied by all applicable ad- not exceed the adjusted compression design value per-justment factors except the column stability factor, ap- pendicular to grain, fc Fc'. When calculating bearingplies to end-to-end bearing of compression members area at the ends of bending members, no allowanceprovided there is adequate lateral support and the end shall be made for the fact that as the member bends,cuts are accurately squared and parallel. pressure upon the inner edge of the bearing is greater 3.10.1.3 When fc > (0.75)(Fc*) bearing shall be on a than at the member end.metal plate or strap, or on other equivalently durable,rigid, homogeneous material with sufficient stiffness todistribute the applied load. Where a rigid insert is re-quired for end-to-end bearing of compression members, Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL24 DESIGN PROVISIONS AND EQUATIONS

Reference compression design values perpendicular

to grain, Fc, apply to bearings of any length at the endsof a member, and to all bearings 6" or more in length atany other location. For bearings less than 6" in lengthand not nearer than 3" to the end of a member, the ref-erence compression design value perpendicular tograin, Fc, shall be permitted to be multiplied by thefollowing bearing area factor, Cb: b 0.375 Cb (3.10-2) b

where: b = bearing length measured parallel to grain, in.

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4.1 General4.1.1 Scope roof, floor, or wall membrane. Decking is graded for application in the flatwise direction, with the wide face Chapter 4 applies to engineering design with sawn of the decking in contact with the supporting members,lumber. Design procedures, reference design values, as normally installed.and other information herein apply only to lumbercomplying with the requirements specified below. 4.1.4 Moisture Service Condition of Lumber4.1.2 Identification of Lumber The reference design values for lumber specified 4.1.2.1 When the reference design values specified herein are applicable to lumber that will be used underherein are used, the lumber, including end-jointed or dry service conditions such as in most covered struc-edge-glued lumber, shall be identified by the grade tures, where the moisture content in use will be a maxi-mark of, or certificate of inspection issued by, a lumber mum of 19%, regardless of the moisture content at thegrading or inspection bureau or agency recognized as time of manufacture. For lumber used under conditionsbeing competent (see Reference 31). A distinct grade where the moisture content of the wood in service willmark of a recognized lumber grading or inspection bu- exceed 19% for an extended period of time, the designreau or agency, indicating that joint integrity is subject values shall be multiplied by the wet service factors, CM,to qualification and quality control, shall be applied to specified in Tables 4A, 4B, 4C, 4D, 4E, and 4F.glued lumber products. 4.1.2.2 Lumber shall be specified by commercialspecies and grade names, or by required levels of de- 4.1.5 Lumber Sizessign values as listed in Tables 4A, 4B, 4C, 4D, 4E, and 4.1.5.1 Lumber sizes referred to in this Specifica-4F (published in the Supplement to this Specification). tion are nominal sizes. Computations to determine the required sizes of members shall be based on the net di-4.1.3 Definitions mensions (actual sizes) and not the nominal sizes. The dressed sizes specified in Reference 31 shall be ac- 4.1.3.1 Structural sawn lumber consists of lumber cepted as the minimum net sizes associated with nomi-classifications known as Dimension, Beams and nal dimensions (see Table 1A in the Supplement to thisStringers, Posts and Timbers, and Decking, with Specification).design values assigned to each grade. 4.1.5.2 For 4" (nominal) or thinner lumber, the net 4.1.3.2 Dimension refers to lumber from 2" to 4" DRY dressed sizes shall be used in all computations of(nominal) thick, and 2" (nominal) or more in width. structural capacity regardless of the moisture content atDimension lumber is further classified as Structural the time of manufacture or use.Light Framing, Light Framing, Studs, and Joists and 4.1.5.3 For 5" (nominal) and thicker lumber, the netPlanks (see References 42, 43, 44, 45, 46, 47, and 49 GREEN dressed sizes shall be used in computations offor additional information). structural capacity regardless of the moisture content at 4.1.3.3 Beams and Stringers refers to lumber of the time of manufacture or use.rectangular cross section, 5" (nominal) or more thick, 4.1.5.4 Where a design is based on rough sizes orwith width more than 2" greater than thickness, graded special sizes, the applicable moisture content and sizewith respect to its strength in bending when loaded on used in design shall be clearly indicated in plans orthe narrow face. specifications. 4.1.3.4 Posts and Timbers refers to lumber ofsquare or approximately square cross section, 5" x 5" 4.1.6 End-Jointed or Edge-Glued(nominal) and larger, with width not more than 2" Lumbergreater than thickness, graded primarily for use as postsor columns carrying longitudinal load. Reference design values for sawn lumber are appli- 4.1.3.5 Decking refers to lumber from 2" to 4" cable to structural end-jointed or edge-glued lumber of(nominal) thick, tongued and grooved, or grooved for the same species and grade. Such use shall include, butspline on the narrow face, and intended for use as a Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 27

not be limited to light framing, studs, joists, planks, and values for the regraded material shall apply (see Refer-decking. When finger jointed lumber is marked STUD ences 16, 42, 43, 44, 45, 46, 47, and 49).USE ONLY or VERTICAL USE ONLY such lum- 4.1.7.2 When sawn lumber is cross cut to shorterber shall be limited to use where any bending or tension lengths, the requirements of 4.1.7.1 shall not apply, ex-stresses are of short duration. cept for reference bending design values for those Beam and Stringer grades where grading provisions for4.1.7 Resawn or Remanufactured the middle 1/3 of the length of the piece differ from grading provisions for the outer thirds.Lumber

4.1.7.1 When structural lumber is resawn or re-

SAWN LUMBER4.2.1 Reference Design Values evaluated lumber in Table 4C are determined by visual grading and nondestructive pretesting of individual Reference design values for visually graded lumber pieces.and for mechanically graded dimension lumber arespecified in Tables 4A, 4B, 4C, 4D, 4E, and 4F (pub- 4.2.4 Modulus of Elasticity, Elished in the Supplement to this Specification). The ref-erence design values in Tables 4A, 4B, 4C, 4D, 4E, and 4.2.4.1 Average Values. Reference design values4F are taken from the published grading rules of the for modulus of elasticity assigned to the visually gradedagencies cited in References 42, 43, 44, 45, 46, 47, and species and grades of lumber listed in Tables 4A, 4B,49. 4C, 4D, 4E, and 4F are average values which conform to ASTM Standards D 245 and D 1990. Adjustments in4.2.2 Other Species and Grades modulus of elasticity have been taken to reflect in- creases for seasoning, increases for density where ap- Reference design values for species and grades of plicable, and, where required, reductions have beenlumber not otherwise provided herein shall be estab- made to account for the effect of grade upon stiffness.lished in accordance with appropriate ASTM standards Reference modulus of elasticity design values are basedand other technically sound criteria (see References 16, upon the species or species group average in accor-18, 19, and 31). dance with ASTM Standards D 1990 and D 2555. 4.2.4.2 Special Uses. Average reference modulus of elasticity design values listed in Tables 4A, 4B, 4C, 4D,4.2.3 Basis for Reference Design 4E, and 4F are to be used in design of repetitive mem-Values ber systems and in calculating the immediate deflection of single members which carry their full design load. In 4.2.3.1 The reference design values in Tables 4A, special applications where deflection is a critical factor,4B, 4C, 4D, 4E, and 4F are for the design of structures or where amount of deformation under long-term load-where an individual member, such as a beam, girder, ing must be limited, the need for use of a reducedpost or other member, carries or is responsible for car- modulus of elasticity design value shall be determined.rying its full design load. For repetitive member uses See Appendix F for provisions on design value adjust-see 4.3.9. ments for special end use requirements. 4.2.3.2 Visually Graded Lumber. Reference designvalues for visually graded lumber in Tables 4A, 4B, 4C, 4.2.5 Bending, Fb4D, 4E, and 4F are based on the provisions of ASTMStandards D 245 and D 1990. 4.2.5.1 Dimension Grades. Adjusted bending de- 4.2.3.3 Machine Stress Rated (MSR) Lumber and sign values for Dimension grades apply to membersMachine Evaluated Lumber (MEL). Reference design with the load applied to either the narrow or wide face.values for machine stress rated lumber and machine Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL28 SAWN LUMBER

values for Decking grades apply only when the load is to Grain, Fcapplied to the wide face. 4.2.5.3 Post and Timber Grades. Adjusted bending For sawn lumber, the reference compression designdesign values for Post and Timber grades apply to values perpendicular to grain are based on a deforma-members with the load applied to either the narrow or tion limit that has been shown by experience to providewide face. for adequate service in typical wood frame construc- 4.2.5.4 Beam and Stringer Grades. Adjusted bend- tion. The reference compression design values perpen-ing design values for Beam and Stringer grades apply dicular to grain specified in Tables 4A, 4B, 4C, 4D, 4E,to members with the load applied to the narrow face. and 4F are species group average values associatedWhen Post and Timber sizes of lumber are graded to with a deformation level of 0.04" for a steel plate onBeam and Stringer grade requirements, design values wood member loading condition. One method for limit-for the applicable Beam and Stringer grades shall be ing deformation in special applications where it is criti-used. Such lumber shall be identified in accordance cal, is use of a reduced compression design value per-with 4.1.2.1 as conforming to Beam and Stringer pendicular to grain. The following equation shall begrades. used to calculate the compression design value perpen- 4.2.5.5 Continuous or Cantilevered Beams. When dicular to grain for a reduced deformation level ofBeams and Stringers are used as continuous or cantile- 0.02":vered beams, the design shall include a requirementthat the grading provisions applicable to the middle 1/3 Fc0.02 = 0.73 Fc (4.2-1)of the length (see References 42, 43, 44, 45, 46, 47, and where:49) shall be applied to at least the middle 2/3 of thelength of pieces to be used as two span continuous Fc0.02 = compression perpendicular to grain designbeams, and to the entire length of pieces to be used over value at 0.02" deformation limit, psithree or more spans or as cantilevered beams. Fc = reference compression perpendicular to grain design value at 0.04" deformation limit (as published in Tables 4A, 4B, 4C, 4D, 4E, and 4F), psi

Fv' = Fv x CD CM Ct - - - Ci - - - - 2.88 0.75

Fc' = Fc x CD CM Ct - CF - Ci - CP - - 2.40 0.90

Fc' = Fc x - CM Ct - - - Ci - - - Cb 1.67 0.90 -

Emin' = Emin x - CM Ct - - - Ci - - CT - 1.76 0.85 -

4.3.5 Beam Stability Factor, CL beams loaded in the plane of the diagonal, the size fac- tor shall be determined in accordance with 4.3.6.2 on Reference bending design values, Fb, shall be mul- the basis of an equivalent conventionally loaded square tiplied by the beam stability factor, CL, specified in beam of the same cross-sectional area. 3.3.3. 4.3.6.4 Reference bending design values for all species of 2" thick or 3" thick Decking, except Red- wood, shall be multiplied by the size factors specified 4.3.6 Size Factor, CF in Table 4E. 4.3.6.1 Reference bending, tension, and compres- sion parallel to grain design values for visually graded 4.3.7 Flat Use Factor, Cfu dimension lumber 2" to 4" thick shall be multiplied by the size factors specified in Tables 4A and 4B. When sawn lumber 2" to 4" thick is loaded on the 4.3.6.2 Where the depth of a rectangular sawn lum- wide face, multiplying the reference bending design ber bending member 5" or thicker exceeds 12", the ref- value, Fb, by the flat use factors, Cfu, specified in Tables erence bending design values, Fb, in Table 4D shall be 4A, 4B, 4C, and 4F, shall be permitted. multiplied by the following size factor: 4.3.8 Incising Factor, CiCF (12 / d)1 9 1.0 (4.3-1) 4.3.6.3 For beams of circular cross section with a Reference design values shall be multiplied by the diameter greater than 13.5", or for 12" or larger square following incising factor, Ci, when dimension lumber is incised parallel to grain a maximum depth of 0.4", a Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL30 SAWN LUMBER

maximum length of 3/8", and density of incisions up to by the buckling stiffness factor, CT, as specified in1100/ft2. Incising factors shall be determined by test or 4.4.2.by calculation using reduced section properties for in-cising patterns exceeding these limits. 4.3.12 Bearing Area Factor, Cb

Reference design values apply to sawn lumber

4.3.9 Repetitive Member Factor, Cr pressure-treated by an approved process and preserva- tive (see Reference 30). Load duration factors greater Reference bending design values, Fb, in Tables 4A, than 1.6 shall not apply to structural members pressure-4B, 4C, and 4F for dimension lumber 2" to 4" thick treated with water-borne preservatives.shall be multiplied by the repetitive member factor, Cr= 1.15, where such members are used as joists, truss 4.3.14 Format Conversion Factor,chords, rafters, studs, planks, decking, or similar mem- KF (LRFD Only)bers which are in contact or spaced not more than 24"on center, are not less than three in number and are For LRFD, reference design values shall be multi-joined by floor, roof or other load distributing elements plied by the format conversion factor, KF, specified inadequate to support the design load. (A load distribut- Table 4.3.1.ing element is any adequate system that is designed orhas been proven by experience to transmit the designload to adjacent members, spaced as described above, 4.3.15 Resistance Factor, (LRFDwithout displaying structural weakness or unacceptable Only)deflection. Subflooring, flooring, sheathing, or othercovering elements and nail gluing or tongue-and- For LRFD, reference design values shall be multi-groove joints, and through nailing generally meet these plied by the resistance factor, , specified in Tablecriteria.) Reference bending design values in Table 4E 4.3.1.for visually graded Decking have already been multi-plied by Cr = 1.15. 4.3.16 Time Effect Factor, (LRFD Only)4.3.10 Column Stability Factor, CP For LRFD, reference design values shall be multi- Reference compression design values parallel to plied by the time effect factor, , specified in Appendixgrain, Fc, shall be multiplied by the column stability N.3.3.factor, CP, specified in 3.7.

4.3.11 Buckling Stiffness Factor,

CT

Reference modulus of elasticity for beam and col-

umn stability, Emin, shall be permitted to be multiplied

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4.4 Special Design Considerations

4.4.1 Stability of Bending 4.4.2 Wood TrussesMembers 4.4.2.1 Increased chord stiffness relative to axial 4.4.1.1 Sawn lumber bending members shall be de- loads where a 2" x 4" or smaller sawn lumber trusssigned in accordance with the lateral stability calcula- compression chord is subjected to combined flexuretions in 3.3.3 or shall meet the lateral support require- and axial compression under dry service condition andments in 4.4.1.2 and 4.4.1.3. has 3/8" or thicker plywood sheathing nailed to the nar- row face of the chord in accordance with code required 4.4.1.2 As an alternative to 4.4.1.1, rectangularsawn lumber beams, rafters, joists, or other bending roof sheathing fastener schedules (see References 32, 4members, shall be designed in accordance with the fol- 33, and 34), shall be permitted to be accounted for bylowing provisions to provide restraint against rotation multiplying the reference modulus of elasticity design

SAWN LUMBERor lateral displacement. If the depth to breadth, d/b, value for beam and column stability, Emin, by the buck-based on nominal dimensions is: ling stiffness factor, CT, in column stability calculations (a) d/b 2; no lateral support shall be required. (see 3.7 and Appendix H). When e < 96", CT shall be (b) 2 < d/b 4; the ends shall be held in position, calculated as follows: as by full depth solid blocking, bridging, hang- KM e ers, nailing, or bolting to other framing mem- CT 1 (4.4-1) KTE bers, or other acceptable means. (c) 4 < d/b 5; the compression edge of the mem- where: ber shall be held in line for its entire length to e = effective column length of truss compres- prevent lateral displacement, as by adequate sheathing or subflooring, and ends at point of sion chord (see 3.7), in. bearing shall be held in position to prevent ro- KM = 2300 for wood seasoned to 19% moisture tation and/or lateral displacement. content or less at the time of plywood at- (d) 5 < d/b 6; bridging, full depth solid blocking tachment. or diagonal cross bracing shall be installed at intervals not exceeding 8 feet, the compression = 1200 for unseasoned or partially seasoned edge of the member shall be held in line as by wood at the time of plywood attachment. adequate sheathing or subflooring, and the ends at points of bearing shall be held in position to KT = 1 1.645(COVE) prevent rotation and/or lateral displacement. = 0.59 for visually graded lumber (e) 6 < d/b 7; both edges of the member shall be held in line for their entire length and ends at = 0.75 for machine evaluated lumber (MEL) points of bearing shall be held in position to = 0.82 for products with COVE 0.11 (see prevent rotation and/or lateral displacement. Appendix F.2) 4.4.1.3 If a bending member is subjected to bothflexure and axial compression, the depth to breadth ra- When e > 96", CT shall be calculated based on e =tio shall be no more than 5 to 1 if one edge is firmly 96".held in line. If under all combinations of load, the un- 4.4.2.2 For additional information concerning metalbraced edge of the member is in tension, the depth to plate connected wood trusses see Reference 9.breadth ratio shall be no more than 6 to 1.

4.4.3 Notches Figure 4A Notch Limitations for

4.4.3.1 End notches, located at the ends of sawn Sawn Lumber Beamslumber bending members for bearing over a support,shall be permitted, and shall not exceed 1/4 the beamdepth (see Figure 4A). 4.4.3.2 Interior notches, located in the outer thirdsof the span of a single span sawn lumber bending mem-ber, shall be permitted, and shall not exceed 1/6 thedepth of the member. Interior notches on the tensionside of 3-" or greater thickness (4" nominal thickness)sawn lumber bending members are not permitted (seeFigure 4A). 4.4.3.3 See 3.1.2 and 3.4.3 for effect of notches onstrength.

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5.1 General5.1.1 Scope Table 5.1.3 Net Finished Widths of 5.1.1.1 Chapter 5 applies to engineering design Structural Gluedwith structural glued laminated timber. Basic require- Laminated Timbersments are provided in this Specification; for additional Nominal Width ofdetail, see Reference 52. Laminations 3 4 6 8 10 12 14 16 5.1.1.2 Design procedures, reference design values (in.)and other information provided herein apply only to Western Speciesstructural glued laminated timber conforming to all per- Net 2- 3-1/8 5-1/8 6- 8- 10- 12- 14- Finishedtinent provisions of the specifications referenced in the Width (in.) Southern Pinefootnotes to Tables 5A, 5B, 5C, and 5D and produced 2- 3-1/8 5-1/8 6- 8- 10- 12- 14-in accordance with ANSI/AITC A190.1. 5.1.4 Service Conditions5.1.2 Definition 5.1.4.1 Reference design values for dry service The term structural glued laminated timber refers conditions shall apply when the moisture content into an engineered, stress rated product of a timber lami- service is less than 16%, as in most covered structures.nating plant, comprising assemblies of specially se- 5.1.4.2 Reference design values for glued laminatedlected and prepared wood laminations bonded together timber shall be multiplied by the wet service factors,with adhesives. The grain of all laminations is ap- CM, specified in Tables 5A, 5B, 5C, and 5D when theproximately parallel longitudinally. The separate lami- moisture content in service is 16% or greater, as maynations shall not exceed 2" in net thickness and are occur in exterior or submerged construction, or humidpermitted to be comprised of: environments. one piece pieces joined end-to-end to form any length pieces placed or glued edge-to-edge to make wider ones pieces bent to curved form during gluing.

5.1.3 Standard Sizes

5.1.3.1 Normal standard finished widths of struc-

tural glued laminated members shall be as shown inTable 5.1.3. This Specification is not intended to pro-hibit other finished widths where required to meet thesize requirements of a design or to meet other specialrequirements. 5.1.3.2 The length and net dimensions of all mem-bers shall be specified. Additional dimensions neces-sary to define non-prismatic members shall be speci-fied.

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5.2 Reference Design Values

5.2.1 Reference Design Values bending. The top side of unbalanced members is re- quired to be marked TOP by the manufacturer. Reference design values for softwood and hard-wood structural glued laminated timber are specified in 5.2.4 Bending, Fbx+, Fbx-, FbyTables 5A, 5B, 5C, and 5D (published in a separateSupplement to this Specification). The reference design The reference bending design values, Fbx+ and Fbx-,values in Tables 5A, 5B, 5C, and 5D are a compilation shall apply to members with loads causing bendingof the reference design values provided in the specifica- about the x-x axis. The reference bending design valuetions referenced in the footnotes to the tables. for positive bending, Fbx+, shall apply for bending stresses causing tension at the bottom of the beam. The5.2.2 Orientation of Member reference bending design value for negative bending, Fbx-, shall apply for bending stresses causing tension at 5 Reference design values for structural glued lami- the top of the beam.nated timber are dependent on the orientation of the The reference bending design value, Fby, shall ap-

STRUCTURAL GLUED LAMINATED TIMBER

laminations relative to the applied loads. Subscripts are ply to members with loads causing bending about the y-used to indicate design values corresponding to a given y axis.orientation. The orientations of the cross-sectional axesfor structural glued laminated timber are shown in Fig- 5.2.5 Compression Perpendicularure 5A. The x-x axis runs parallel to the wide face of to Grain, Fcx, Fcythe laminations. The y-y axis runs perpendicular to thewide faces of the laminations. The reference compression design value perpen- dicular to grain, Fcx, shall apply to members with bear-Figure 5A Axis Orientations ing loads on the wide faces of the laminations. The reference compression design value perpen- dicular to grain, Fcy, shall apply to members with bear- ing loads on the narrow edges of the laminations. The reference compression design values perpen- dicular to grain are based on a deformation limit of 0.04" obtained from testing in accordance with ASTM D143. The compression perpendicular to grain stress associated with a 0.02" deformation limit shall be per- mitted to be calculated as 73% of the reference value (see also 4.2.6).

5.2.6 Shear Parallel to Grain, Fvx,

Fvy5.2.3 Balanced and UnbalancedLayups The reference shear design value parallel to grain, Fvx shall apply to members with shear loads causing Structural glued laminated timbers are permitted to bending about the x-x axis. The reference shear designbe assembled with laminations of the same lumber value parallel to grain, Fvy, shall apply to members withgrades placed symmetrically or asymmetrically about shear loads causing bending about the y-y axis.the neutral axis of the member. Symmetrical layups are The reference shear design values parallel to grainreferred to as balanced and have the same design val- shall apply to prismatic members except those subjectues for positive and negative bending. Asymmetrical to impact or repetitive cyclic loads. For non-prismaticlayups are referred to as unbalanced and have lower members and for all members subject to impact or re-design values for negative bending than for positive petitive cyclic loads, the reference shear design values Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL36 STRUCTURAL GLUED LAMINATED TIMBER

parallel to grain shall be multiplied by the shear reduc- 5.2.8 Radial Tension, Frttion factor specified in 5.3.10. This reduction shall alsoapply to the design of connections transferring loads For curved bending members, the following refer-through mechanical fasteners (see 3.4.3.3, 10.1.2, and ence radial tension design values perpendicular to10.2.2). grain, Frt, shall apply: Prismatic members shall be defined as straight orcambered members with constant cross-section. Non- Table 5.2.8 Radial Tension Designprismatic members include, but are not limited to: Values, Frt, for Curvedarches, tapered beams, curved beams, and notched Membersmembers. The reference shear design value parallel to grain, Southern Pine all loading Frt = (1/3)FvxCvrFvy, is tabulated for members with four or more lamina- conditionstions. For members with two or three laminations, the Douglas Fir-Larch, wind or Frt = (1/3)FvxCvrreference design value shall be multiplied by 0.84 or Douglas Fir South, earthquake0.95, respectively. Hem-Fir, Western loading Woods, and Canadian other types Frt = 15 psi softwood species of loading5.2.7 Modulus of Elasticity, E x ,E x min, Ey, Ey min 5.2.9 Radial Compression, Frc The reference modulus of elasticity, Ex, shall beused for determination of deflections due to bending For curved bending members, the reference radialabout the x-x axis. compression design value, Frc, shall be taken as the ref- The reference modulus of elasticity, Ex min, shall be erence compression perpendicular to grain design valueused for beam and column stability calculations for on the side face, Fcy.members buckling about the x-x axis. The reference modulus of elasticity, Ey, shall be 5.2.10 Other Species and Gradesused for determination of deflections due to bendingabout the y-y axis. Reference design values for species and grades of The reference modulus of elasticity, Ey min, shall be structural glued laminated timber not otherwise pro-used for beam and column stability calculations for vided herein shall be established in accordance withmembers buckling about the y-y axis. Reference 22, or shall be based on other substantiated For the calculation of extensional deformations, the information from an approved source.axial modulus of elasticity shall be permitted to be es-timated as Eaxial = 1.05Ey.

5.3.7 Flat Use Factor, Cfu 5.3.9 Stress Interaction Factor, CI

When structural glued laminated timber is loaded in For the tapered portion of bending members ta-bending about the y-y axis and the member dimension pered on the compression face, the reference bendingparallel to the wide face of the laminations, dy (see Fig- design value, Fbx, shall be multiplied by the followingure 5B), is less than 12", the reference bending design stress interaction factor:value, Fby, shall be permitted to be multiplied by the flat 1 (5.3-4)use factor, Cfu, specified in Tables 5A, 5B, 5C, and 5D, CI = 2 2or as calculated by the following formula: F tan Fb tan 2 1+ b FvCvr Fc

12 1/9 (5.3-2) where: Cfu = d y = angle of taper, degrees

Figure 5B Depth, dy, for Flat Use For members tapered on the compression face, the stress interaction factor, CI, shall not apply simultane- Factor ously with the volume factor, CV, therefore, the lesser of these adjustment factors shall apply. For the tapered portion of bending members ta- pered on the tension face, the reference bending design value, Fbx, shall be multiplied by the following stress interaction factor:

= 0.29(de/Rm) + 0.32 tan1.2T de = depth at the ends of the member, in.

1.0 for uniformly loaded members where B = soffit slope at the ends of the member, dc/Rm 0.3 degrees = 1.0 for members subject to constant The horizontal deflection at the supports of sym- moment metrical double-tapered curved beams shall be permit- = span length, in. ted to be estimated as:

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facturers recommendations to account for the removal

Figure 5C Double-Tapered Curved of high grade material near the surface of the member. Bending Member 5.4.4.2 Tapered straight beams shall be designed for shear strength in accordance with 3.4, except that the provisions of 3.4.3.1 shall not apply. The shear re- t /2 /2 t duction factor from 5.3.10 shall apply. c c

5.4.4.3 The deflection of tapered straight beams

dt d c/2 T shall be determined in accordance with 3.5, except thatde B P.T. Rm hs P.T. the maximum deflection of a tapered straight beam sub- R B R ject to uniform loads shall be permitted to be calculated as equivalent to the depth, dequiv, of an equivalent pris- matic member of the same width where:5.4.3 Lateral Stability for TudorArches dequiv C dt de (5.4-6)

The ratio of tangent point depth to breadth (d/b) of where:

5tudor arches (see Figure 5D) shall not exceed 6, based de = depth at the small end of the member, in.on actual dimensions, when one edge of the arch is

STRUCTURAL GLUED LAMINATED TIMBER

braced by decking fastened directly to the arch, or Cdt = empirical constant derived from relation-braced at frequent intervals as by girts or roof purlins. ship of equations for deflection of taperedWhere such lateral bracing is not present, d/b shall not straight beams and prismatic beams.exceed 5. Arches shall be designed for lateral stabilityin accordance with the provisions of 3.7 and 3.9.2. For symmetrical double-tapered beams: Cdt = 1 + 0.66Cy when 0 < Cy 1Figure 5D Tudor Arch Cdt = 1 + 0.62Cy when 1 < Cy 3

5.4.5 Notches laminated timber bending member shall

not exceed 2/3 the depth of the member 5.4.5.1 The tension side of structural glued lami- and the length shall not exceed three timesnated timber bending members shall not be notched, the depth of the member, 3d. For taperedexcept at ends of members for bearing over a support, beams where the taper extends into theand notch depth shall not exceed the lesser of 1/10 the middle 1/3 of the span, design shall be indepth of the member or 3". accordance with 5.4.4. 5.4.5.2 The compression side of structural gluedlaminated timber bending members shall not be 5.4.5.3 Notches shall not be permitted on both thenotched, except at ends of members, and the notch tension and compression face at the same cross-section.depth on the compression side shall not exceed 2/5 the 5.4.5.4 See 3.1.2 and 3.4.3 for the effect of notchesdepth of the member. Compression side end-notches on strength. The shear reduction factor from 5.3.10shall not extend into the middle 1/3 of the span. shall apply for the evaluation of members at notches. Exception: A taper cut on the compres- sion edge at the end of a structural glued

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air dried timber poles and piles, and shall be adjusted in 6.1.2.1 The procedures and reference design values accordance with 6.3.5 when conditioned and treated byherein apply only to timber piles conforming to appli- an approved process (see Reference 30). Load durationcable provisions of ASTM Standard D 25 and only to factors greater than 1.6 shall not apply to structuralpoles conforming to applicable provisions of ASTM members pressure-treated with water-borne preserva-Standard D 3200. tives. 6.1.2.2 Specifications for round timber poles and 6.1.4.2 Untreated, timber poles and piles shall notpiles shall include the standard for preservative treat- be used unless the cutoff is below the lowest groundment, pile length, and nominal tip circumference or water level expected during the life of the structure, butnominal circumference 3 feet from the butt. Specifica- in no case less than 3 feet below the existing groundtions for piles shall state whether piles are to be used as water level unless approved by the authority havingfoundation piles, land and fresh water piles, or marine jurisdiction.piles.

6.2 Reference Design Values

6.2.1 Reference Design Values in Table 6B are based on provisions of ASTM Standard D 3200. 6.2.1.1 Reference design values for round timberpiles are specified in Table 6A (published in the Sup- 6.2.2 Other Species or Gradesplement to this Specification). Reference design valuesin Table 6A are based on the provisions of ASTM Reference design values for piles of other speciesStandard D 2899. or grades shall be determined in accordance with 6.2.1.2 Reference design values for round timber ASTM Standard D 2899.poles are specified in Table 6B (published in the Sup-plement to this Specification). Reference design values

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Emin' = Emin x - Ct - - - - - - 1.76 0.85 -

6.3.5 Condition Treatment Factor, where:

Cct Lc = length from tip of pile to critical section, ft The increase for location of critical section shall Reference design values are based on air dried con- not exceed 10% for any pile or pole (Ccs 1.10). Theditioning. If kiln-drying, steam-conditioning, or boul- critical section factors, Ccs, are independent of taperedtonizing is used prior to treatment (see reference 20) column provisions in 3.7.2 and both shall be permittedthen the reference design values shall be multiplied by to be used in design calculations.the condition treatment factors, Cct, in Table 6.3.5.

grain, Fc, for round timber piles and poles are based on KF (LRFD Only)the strength at the tip of the pile. Reference compres-sion design values parallel to grain, Fc, in Table 6A and For LRFD, reference design values shall be multi-Table 6B shall be permitted to be multiplied by the plied by the format conversion factor, KF, specified incritical section factor. The critical section factor, Ccs, Table 6.3.1.shall be determined as follows:

Ccs = 1.0 + 0.004Lc (6.3-1)

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6.3.13 Resistance Factor, (LRFD 6.3.14 Time Effect Factor, (LRFD

Only) Only)

For LRFD, reference design values shall be multi- For LRFD, reference design values shall be multi-plied by the resistance factor, , specified in Table plied by the time effect factor, , specified in Appendix6.3.1. N.3.3.

Chapter 7 applies to engineering design with pre- When the design procedures and other informa-fabricated wood I-joists. Basic requirements are pro- tion provided herein are used, the prefabricated woodvided in this Specification. Design procedures and other I-joists shall be identified with the manufacturers nameinformation provided herein apply only to prefabricated and the quality assurance agencys name.wood I-joists conforming to all pertinent provisions ofASTM D 5055. 7.1.4 Service Conditions

7.1.2 Definition Reference design values reflect dry service condi-

tions, where the moisture content in service is less than The term prefabricated wood I-joist refers to a 16%, as in most covered structures. Prefabricated woodstructural member manufactured using sawn or struc- I-joists shall not be used in higher moisture servicetural composite lumber flanges and wood structural conditions unless specifically permitted by the prefabri-panel webs bonded together with exterior exposure ad- cated wood I-joist manufacturer.hesives, forming an I cross-sectional shape.

7.3.3 Wet Service Factor, CM

Reference design values for prefabricated wood

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Table 7.3.1 Applicability of Adjustment Factors

for Prefabricated Wood I-Joists

ASD LRFD ASD and LRFD only only

Format Conversion Factor

Repetitive Member Factor

Resistance Factor Beam Stability Factor Load Duration Factor

Temperature Factor Wet Service Factor

Time Effect Factor

KF

Mr' = Mr x CD CM Ct CL Cr KF 0.85

Vr' = Vr x CD CM Ct - - KF 0.75

Rr' = Rr x CD CM Ct - - KF 0.75 7 EI' = EI x - CM Ct - - - - -

PREFABRICATED WOOD I-JOISTS

(EI)min' = (EI)min x - CM Ct - - KF 0.85 -

K' = K x - CM Ct - - - - -

7.3.5 Beam Stability Factor, CL ricated wood I-joists shall be provided with lateral sup- port at points of bearing to prevent rotation. 7.3.5.1 Lateral stability of prefabricated wood I-joists shall be considered. 7.3.6 Repetitive Member Factor, Cr 7.3.5.2 When the compression flange of a prefabri-cated wood I-joist is supported throughout its length to For prefabricated wood I-joists with structuralprevent lateral displacement, and the ends at points of composite lumber flanges or sawn lumber flanges, ref-bearing have lateral support to prevent rotation, CL=1.0. erence moment design resistances shall be multiplied by the repetitive member factor, Cr = 1.0. 7.3.5.3 When the compression flange of a prefabri-cated wood I-joist is not supported throughout its length 7.3.7 Pressure-Preservativeto prevent lateral displacement, one acceptable methodis to design the prefabricated wood I-joist compression Treatmentflange as a column in accordance with the procedure of3.7.1 using the section properties of the compression Adjustments to reference design values to accountflange only. The compression flange shall be evaluated for the effects of pressure-preservative treatment shallas a column continuously restrained from buckling in be in accordance with information provided by the pre-the plane of the web. CP of the compression flange shall fabricated wood I-joist manufacturer.be used as CL of the prefabricated wood I-joist. Prefab-

7.3.9 Resistance Factor, (LRFD

For LRFD, reference design values shall be multi-

7.4 Special Design Considerations

7.4.1 Bearing obtained from the prefabricated wood I-joist manufac- turers literature or code evaluation reports. Reference bearing design values, as a function ofbearing length, for prefabricated wood I-joists with and 7.4.4 Notcheswithout web stiffeners shall be obtained from the pre-fabricated wood I-joist manufacturers literature or Notched flanges at or between bearings signifi-code evaluation reports. cantly reduces prefabricated wood I-joist capacity and is beyond the scope of this document. See the manufac-7.4.2 Load Application turer for more information.

Prefabricated wood I-joists act primarily to resist 7.4.5 Deflection

loads applied to the top flange. Web stiffener require-ments, if any, at concentrated loads applied to the top Both bending and shear deformations shall be con-flange and design values to resist concentrated loads sidered in deflection calculations, in accordance withapplied to the web or bottom flange shall be obtained the prefabricated wood I-joist manufacturers literaturefrom the prefabricated wood I-joist manufacturers lit- or code evaluation reports.erature or code evaluation reports. 7.4.6 Vertical Load Transfer7.4.3 Web Holes Prefabricated wood I-joists supporting bearing The effects of web holes on strength shall be ac- walls located directly above the prefabricated wood I-counted for in the design. Determination of critical joist support require rim joists, blocking panels, orshear at a web hole shall consider load combinations of other means to directly transfer vertical loads from the1.4.4 and partial span loadings defined as live or snow bearing wall to the supporting structure below.loads applied from each adjacent bearing to the oppo-site edge of a rectangular hole (centerline of a circular 7.4.7 Shearhole). The effects of web holes on deflection are negli-gible when the number of holes is limited to 3 or less Provisions of 3.4.3.1 for calculating shear force,per span. Reference design values for prefabricated V, shall not be used for design of prefabricated woodwood I-joists with round or rectangular holes shall be I-joist bending members.

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8.1 General8.1.1 Scope 8.1.2.3 The term structural composite lumber re- fers to either laminated veneer lumber or parallel strand Chapter 8 applies to engineering design with struc- lumber. These materials are structural members bondedtural composite lumber. Basic requirements are pro- with an exterior adhesive.vided in this Specification. Design procedures and otherinformation provided herein apply only to structural 8.1.3 Identificationcomposite lumber conforming to all pertinent provi-sions of ASTM D5456. When the design procedures and other information provided herein are used, the structural composite lum-8.1.2 Definitions ber shall be identified with the manufacturers name and the quality assurance agencys name. 8.1.2.1 The term laminated veneer lumber refersto a composite of wood veneer sheet elements with 8.1.4 Service Conditionswood fiber primarily oriented along the length of themember. Veneer thickness shall not exceed 0.25". Reference design values reflect dry service condi- 8.1.2.2 The term parallel strand lumber refers to a tions, where the moisture content in service is less thancomposite of wood strand elements with wood fibers 16%, as in most covered structures. Structural compos-primarily oriented along the length of the member. The ite lumber shall not be used in higher moisture serviceleast dimension of the strands shall not exceed 0.25" conditions unless specifically permitted by the struc-and the average length shall be a minimum of 150 times tural composite lumber manufacturer.the least dimension.

8.2 Reference Design Values

Reference design values for structural compositelumber shall be obtained from the structural compositelumber manufacturers literature or code evaluationreport. In special applications where deflection is acritical factor, or where deformation under long-termloading must be limited, the need for use of a reducedmodulus of elasticity shall be determined. See Appen-dix F for provisions on adjusted values for special enduse requirements.

shall be laterally supported in accordance with 3.3.3. Reference design values for structural compositelumber are applicable to dry service conditions as 8.3.6 Volume Factor, CVspecified in 8.1.4 where CM = 1.0. When the serviceconditions differ from the specified conditions, adjust- Reference bending design values, Fb, for structuralments for high moisture shall be in accordance with composite lumber shall be multiplied by the volumeinformation provided by the structural composite lum- factor, CV, and shall be obtained from the structuralber manufacturer. composite lumber manufacturers literature or code Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL56 STRUCTURAL COMPOSITE LUMBER

CV, shall not apply simultaneously with the beam sta- Treatmentbility factor, CL (see 3.3.3) and therefore, the lesser ofthese adjustment factors shall apply. When CV > 1.0, Adjustments to reference design values to accountthe volume factor, CV, shall apply simultaneously with for the effects of pressure-preservative treatment shallthe beam stability factor, CL (see 3.3.3). be in accordance with information provided by the structural composite lumber manufacturer.8.3.7 Repetitive Member Factor, Cr 8.3.11 Format Conversion Factor, Reference bending design values, Fb, shall be mul-tiplied by the repetitive member factor, Cr = 1.04, KF (LRFD Only)where such members are used as joists, studs, or similarmembers which are in contact or spaced not more than For LRFD, reference design values shall be multi-24" on center, are not less than 3 in number and are plied by the format conversion factor, KF, specified injoined by floor, roof, or other load distributing elements Table 8.3.1.adequate to support the design load. (A load distribut-ing element is any adequate system that is designed or 8.3.12 Resistance Factor, (LRFDhas been proven by experience to transmit the design Only)load to adjacent members, spaced as described above,without displaying structural weakness or unacceptable For LRFD, reference design values shall be multi-deflection. Subflooring, flooring, sheathing, or other plied by the resistance factor, , specified in Tablecovering elements and nail gluing or tongue-and- 8.3.1.groove joints, and through nailing generally meet thesecriteria.) 8.3.13 Time Effect Factor, (LRFD8.3.8 Column Stability Factor, CP Only)

8.3.9 Bearing Area Factor, Cb

Reference compression design values perpendicular

to grain, Fc, shall be permitted to be multiplied by thebearing area factor, Cb, as specified in 3.10.4.

8.4 Special Design Considerations

8.4.1 Notches side end-notches shall not extend into the middle third of the span. 8.4.1.1 The tension side of structural composite 8.4.1.2 See 3.1.2 and 3.4.3 for effect of notches onbending members shall not be notched, except at ends strength.of members for bearing over a support, and notch depthshall not exceed 1/10 the depth of the member. Thecompression side of structural composite bendingmembers shall not be notched, except at ends of mem-bers, and the notch depth on the compression side shallnot exceed 2/5 the depth of the member. Compression Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 57

9.1 General9.1.1 Scope adhesive. Included under this designation are plywood, oriented strand board (OSB) and composite panels. Chapter 9 applies to engineering design with the These panel products meet the requirements of USDOCfollowing wood structural panels: plywood, oriented PS 1 or PS 2 and are intended for structural use in resi-strand board, and composite panels. Basic requirements dential, commercial, and industrial applications.are provided in this Specification. Design procedures 9.1.3.2 The term composite panel refers to aand other information provided herein apply only to wood structural panel comprised of wood veneer andwood structural panels complying with the require- reconstituted wood-based material and bonded withments specified in this Chapter. waterproof adhesive. 9.1.3.3 The term oriented strand board refers to a mat-formed wood structural panel comprised of thin9.1.2 Identification rectangular wood strands arranged in cross-aligned lay- ers with surface layers normally arranged in the long 9.1.2.1 When design procedures and other informa- panel direction and bonded with waterproof adhesive.tion herein are used, the wood structural panel shall be 9.1.3.4 The term plywood refers to a wood struc-identified for grade and glue type by the trademarks of tural panel comprised of plies of wood veneer arrangedan approved testing and grading agency. in cross-aligned layers. The plies are bonded with an 9.1.2.2 Wood structural panels shall be specified by adhesive that cures on application of heat and pressure.span rating, nominal thickness, exposure rating, andgrade. 9.1.4 Service Conditions9.1.3 Definitions 9.1.4.1 Reference design values reflect dry service conditions, where the moisture content in service is less 9.1.3.1 The term wood structural panel refers to a than 16%, as in most covered structures.wood-based panel product bonded with a waterproof

9.2 Reference Design Values

9.2.1 Panel Stiffness and Strength design values, respectively, on the basis of tabulated design section properties. 9.2.1.1 Reference panel stiffness and strength de-sign values (the product of material and section proper- 9.2.3 Design Thicknessties) shall be obtained from an approved source. 9.2.1.2 Due to the orthotropic nature of panels, ref- Nominal thickness shall be used in design calcula-erence design values shall be provided for the primary tions. The relationships between span ratings andand secondary strength axes. The appropriate reference nominal thicknesses are provided with associated refer-design values shall be applied when designing for each ence design values.panel orientation. When forces act at an angle to theprincipal axes of the panel, the capacity of the panel at 9.2.4 Design Section Propertiesthe angle shall be calculated by adjusting the referencedesign values for the principal axes using principles of Design section properties shall be assigned on theengineering mechanics. basis of span rating or design thickness and are pro- vided on a per-foot-of-panel-width basis.9.2.2 Strength and ElasticProperties

Where required, strength and elastic parameters

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9.3 Adjustment of Reference Design Values

9.3.1 General 9.3.3 Wet Service Factor, CM, and Temperature Factor, Ct Reference design values shall be multiplied by theadjustment factors specified in Table 9.3.1 to determine Reference design values for wood structural panelsadjusted design values. are applicable to dry service conditions as specified in 9.1.4 where CM = 1.0 and Ct = 1.0. When the service9.3.2 Load Duration Factor, CD (ASD conditions differ from the specified conditions, adjust-Only) ments for high moisture and/or high temperature shall be based on information from an approved source. All reference strength design values (FbS, FtA, Fvtv,Fs(Ib/Q), FcA) shall be multiplied by load duration fac-tors, CD, as specified in 2.3.2.

For LRFD, reference design values shall be multi-

plied by the time effect factor, , specified in Appendix N.3.3.

9.4 Design Considerations

9.4.1 Flatwise Bending 9.4.3 Compression in the Plane of the Panel Wood structural panels shall be designed for flex-ure by checking bending moment, shear, and deflection. When wood structural panels are loaded in axialAdjusted planar shear shall be used as the shear resis- compression, the orientation of the primary strengthtance in checking the shear for panels in flatwise bend- axis of the panel with respect to the direction of load-ing. Appropriate beam equations shall be used with the ing, shall be considered in determining the adjusteddesign spans as defined below. compressive capacity. In addition, panels shall be de- (a) Bending moment-distance between center-line signed to prevent buckling. of supports. (b) Shear-clear span. 9.4.4 Planar (Rolling) Shear (c) Deflection-clear span plus the support width The adjusted planar (rolling) shear shall be used in factor. For 2" nominal and 4" nominal framing, design when the shear force is applied in the plane of the support width factor is equal to 0.25" and wood structural panels. 0.625", respectively. 9.4.5 Through-the-Thickness9.4.2 Tension in the Plane of the ShearPanel The adjusted through-the-thickness shear shall be When wood structural panels are loaded in axial used in design when the shear force is applied through-tension, the orientation of the primary strength axis of the-thickness of wood structural panels.the panel with respect to the direction of loading, shallbe considered in determining adjusted tensile capacity. 9.4.6 Bearing The adjusted bearing design value of wood struc- tural panels shall be used in design when the load is applied perpendicular to the panel face. Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 61

10.1 General10.1.1 Scope 10.1.3 Eccentric Connections 10.1.1.1 Chapter 10 applies to the engineering de- Eccentric connections that induce tension stresssign of connections using bolts, lag screws, split ring perpendicular to grain in the wood shall not be usedconnectors, shear plate connectors, drift bolts, drift unless appropriate engineering procedures or tests arepins, wood screws, nails, spikes, timber rivets, spike employed in the design of such connections to insuregrids, or other fasteners in sawn lumber, structural that all applied loads will be safely carried by the mem-glued laminated timber, timber poles, timber piles, bers and connections. Connections similar to those instructural composite lumber, prefabricated wood I- Figure 10A are examples of connections requiring ap-joists, and wood structural panels. Except where spe- propriate engineering procedures or tests.cifically limited elsewhere herein, the provisions ofChapter 10 shall apply to all fastener types covered inChapters 11, 12, and 13. 10.1.4 Mixed Fastener 10.1.1.2 The requirements of 3.1.3, 3.1.4, and 3.1.5 Connectionsshall be accounted for in the design of connections. 10.1.1.3 Connection design provisions in Chapters Methods of analysis and test data for establishing10, 11, 12, and 13 shall not preclude the use of connec- reference design values for connections made withtions where it is demonstrated by analysis based on more than one type of fastener have not been devel-generally recognized theory, full-scale or prototype oped. Reference design values and design value ad-loading tests, studies of model analogues or extensive justments for mixed fastener connections shall be basedexperience in use that the connections will perform sat- on tests or other analysis (see 1.1.1.3).isfactorily in their intended end uses (see 1.1.1.3). 10.1.5 Connection Fabrication10.1.2 Stresses in Members at Reference lateral design values for connections inConnections Chapters 11, 12, and 13 are based on: (a) the assumption that the faces of the members Structural members shall be checked for load carry- are brought into contact when the fasteners areing capacity at connections in accordance with all ap- installed, andplicable provisions of this standard including 3.1.2, (b) allowance for member shrinkage due to sea-3.1.3, and 3.4.3.3. Local stresses in connections using sonal variations in moisture content (seemultiple fasteners shall be checked in accordance with 10.3.3).principles of engineering mechanics. One method fordetermining these stresses is provided in Appendix E.

Figure 10A Eccentric Connections

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10.2 Reference Design Values

10.2.1 Single Fastener tener. Local stresses in connections using multiple fas- teners shall be evaluated in accordance with principlesConnections of engineering mechanics (see 10.1.2). 10.2.1.1 Chapters 11, 12, and 13 contain tabulatedreference design values and design provisions for calcu- 10.2.3 Design of Metal Partslating reference design values for various types of sin-gle fastener connections. Reference design values for Metal plates, hangers, fasteners, and other metalconnections in a given species apply to all grades of parts shall be designed in accordance with applicablethat species unless otherwise indicated. Dowel-type metal design procedures to resist failure in tension,fastener connection reference design values for one shear, bearing (metal on metal), bending, and bucklingspecies of wood are also applicable to other species (see References 39, 40, and 41). When the capacity of ahaving the same or higher dowel bearing strength, Fe. connection is controlled by metal strength rather than 10.2.1.2 Design provisions and reference design wood strength, metal strength shall not be multiplied byvalues for dowel-type fastener connections such as the adjustment factors in this Specification. In addition,bolts, lag screws, wood screws, nails, spikes, drift bolts, metal strength shall not be increased by wind and earth-and drift pins are provided in Chapter 11. quake factors if design loads have already been reduced 10.2.1.3 Design provisions and reference design by load combination factors (see Reference 5 for addi-values for split ring and shear plate connections are pro- tional information).vided in Chapter 12. 10.2.1.4 Design provisions and reference design 10.2.4 Design of Concrete orvalues for timber rivet connections are provided in Masonry PartsChapter 13. 10.2.1.5 Wood to wood connections involving Concrete footers, walls, and other concrete or ma-spike grids for load transfer shall be designed in accor- sonry parts shall be designed in accordance with ac-dance with principles of engineering mechanics (see cepted practices (see References 1 and 2). When theReference 50 for additional information). capacity of a connection is controlled by concrete or masonry strength rather than wood strength, concrete or 1010.2.2 Multiple Fastener masonry strength shall not be multiplied by the adjust-Connections ment factors in this Specification. In addition, concrete or masonry strength shall not be increased by wind and

MECHANICAL CONNECTIONS Where a connection contains two or more fasteners earthquake factors if design loads have already beenof the same type and similar size, each of which exhib- reduced by load combination factors (see Reference 5its the same yield mode (see Appendix I), the total ad- for additional information).justed design value for the connection shall be the sumof the adjusted design values for each individual fas-

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10.3.6 Group Action Factors, Cg Group action factors for various connection geome- tries are provided in Tables 10.3.6A, 10.3.6B, 10.3.6C, 10.3.6.1 Reference lateral design values for split and 10.3.6D. ring connectors, shear plate connectors, or dowel-type 10.3.6.2 For determining group action factors, a fasteners with D 1" in a row shall be multiplied by the row of fasteners is defined as any of the following: following group action factor, Cg: (a) Two or more split rings or shear plate connec- tor units, as defined in 12.1.1, aligned with the 1 R direction of load. Cg m(1 m2n ) EA (10.3-1) n 1 REA mn (1 m) 1 m2n 1 m (b) Two or more dowel-type fasteners of the same

diameter loaded in single or multiple shear and where: aligned with the direction of load. Where fasteners in adjacent rows are staggered and Cg = 1.0 for dowel type fasteners with D < 1/4" the distance between adjacent rows is less than 1/4 the n = number of fasteners in a row distance between the closest fasteners in adjacent rows measured parallel to the rows, the adjacent rows shall E sAs E A be considered as one row for purposes of determining REA = the lesser of or m m E m Am E sAs group action factors. For groups of fasteners having an Em = modulus of elasticity of main member, psi even number of rows, this principle shall apply to each pair of rows. For groups of fasteners having an odd Es = modulus of elasticity of side members, psi number of rows, the most conservative interpretation Am = gross cross-sectional area of main mem- shall apply (see Figure 10B). ber, in.2 10.3.6.3 Gross section areas shall be used, with no reductions for net section, when calculating Am and As As = sum of gross cross-sectional areas of side for determining group action factors. When a member members, in.2 is loaded perpendicular to grain its equivalent cross- sectional area shall be the product of the thickness of m = u u2 1 the member and the overall width of the fastener group s 1 1 (see Figure 10B). Where only one row of fasteners is u = 1 used, the width of the fastener group shall be the mini- 2 E m Am E s As mum parallel to grain spacing of the fasteners. s = center to center spacing between adjacent fasteners in a row, in.

= load/slip modulus for a connection, lbs/in.

= 500,000 lbs/in. for 4" split ring or shear

plate connectors

= 400,000 lbs/in. for 2-1/2" split ring or

2-5/8" shear plate connectors

= (180,000)(D1.5) for dowel-type fasteners in

wood-to-wood connections

= (270,000)(D1.5) for dowel-type fasteners in

wood-to-metal connections

D = diameter of dowel-type fastener, in.

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11.1 General11.1.1 Scope 11.1.3.4 Edge distances, end distances, and fastener spacings shall not be less than the requirements in Ta- Chapter 11 applies to the engineering design of bles 11.5.1A through 11.5.1D.connections using bolts, lag screws, wood screws, nails,spikes, drift bolts, drift pins, or other dowel-type fas- 11.1.4 Lag Screwsteners in sawn lumber, structural glued laminated tim-ber, timber poles, timber piles, structural composite 11.1.4.1 Installation requirements apply to laglumber, prefabricated wood I-joists, and wood struc- screws meeting requirements of ANSI/ASME Standardtural panels. B18.2.1. See Appendix Table L2 for standard hex lag screw dimensions.11.1.2 Terminology 11.1.4.2 Lead holes for lag screws loaded laterally and in withdrawal shall be bored as follows to avoid 11.1.2.1 Edge distance is the distance from the splitting of the wood member during connection fabri-edge of a member to the center of the nearest fastener, cation:measured perpendicular to grain. When a member is (a) The clearance hole for the shank shall have theloaded perpendicular to grain, the loaded edge shall be same diameter as the shank, and the same depthdefined as the edge in the direction toward which the of penetration as the length of unthreadedfastener is acting. The unloaded edge shall be defined shank.as the edge opposite the loaded edge (see Figure 11G). (b) The lead hole for the threaded portion shall 11.1.2.2 End distance is the distance measured have a diameter equal to 65% to 85% of theparallel to grain from the square-cut end of a member to shank diameter in wood with G > 0.6, 60% tothe center of the nearest bolt (see Figure 11G). 75% in wood with 0.5 < G 0.6, and 40% to 11.1.2.3 Spacing is the distance between centers 70% in wood with G 0.5 (see Table 11.3.3A)of fasteners measured along a line joining their centers and a length equal to at least the length of the(see Figure 11G). threaded portion. The larger percentile in each 11.1.2.4 A row of fasteners is defined as two or range shall apply to lag screws of greater di-more fasteners aligned with the direction of load (see ameters.Figure 11G). 11.1.4.3 Lead holes or clearance holes shall not be 11.1.2.5 End distance, edge distance, and spacing required for 3/8" and smaller diameter lag screwsrequirements herein are based on wood properties. loaded primarily in withdrawal in wood with G 0.5Wood-to-metal and wood-to-concrete connections are (see Table 11.3.3A), provided that edge distances, endsubject to placement provisions as shown in 11.5.1, distances, and spacing are sufficient to prevent unusualhowever, applicable end and edge distance and spacing splitting.requirements for metal and concrete, also apply (see 11.1.4.4 The threaded portion of the lag screw shall10.2.3 and 10.2.4). be inserted in its lead hole by turning with a wrench, not by driving with a hammer. 11.1.4.5 No reduction to reference design values is11.1.3 Bolts anticipated if soap or other lubricant is used on the lag 11.1.3.1 Installation requirements apply to bolts meet- screw or in the lead holes to facilitate insertion and toing requirements of ANSI/ASME Standard B18.2.1. See prevent damage to the lag screw.Appendix Table L1 for standard hex bolt dimensions. 11.1.4.6 The minimum length of lag screw penetra- 11.1.3.2 Holes shall be a minimum of 1/32" to a tion, pmin, not including the length of the tapered tip, E,maximum of 1/16" larger than the bolt diameter. Holes of the lag screw into the main member of single shearshall be accurately aligned in main members and side connections and the side members of double shear con-plates. Bolts shall not be forcibly driven. nections shall be 4D. 11.1.3.3 A standard cut washer (Appendix Table 11.1.4.7 Edge distances, end distances, and fastenerL6), or metal plate or metal strap of equal or greater spacings shall not be less than the requirements in Ta-dimensions shall be provided between the wood and the bles 11.5.1A through 11.5.1E.bolt head and between the wood and the nut. Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 73

11.1.5 Wood Screws box, and sinker nail dimensions and Appendix Table L5 for standard post-frame ring shank nail dimensions. 11.1.5.1 Installation requirements apply to wood 11.1.6.2 Threaded, hardened-steel nails, and spikesscrews meeting requirements of ANSI/ASME Standard shall be made of high carbon steel wire, headed,B18.6.1. See Appendix Table L3 for standard wood pointed, annularly or helically threaded, and heat-screw dimensions. treated and tempered to provide greater yield strength 11.1.5.2 Lead holes for wood screws loaded in than for common wire nails of corresponding size.withdrawal shall have a diameter equal to approxi- 11.1.6.3 Reference design values herein apply tomately 90% of the wood screw root diameter in wood nailed and spiked connections either with or withoutwith G > 0.6, and approximately 70% of the wood bored holes. When a bored hole is desired to preventscrew root diameter in wood with 0.5 < G 0.6. Wood splitting of wood, the diameter of the bored hole shallwith G 0.5 (see Table 11.3.3A) is not required to have not exceed 90% of the nail or spike diameter for wooda lead hole for insertion of wood screws. with G > 0.6, nor 75% of the nail or spike diameter for 11.1.5.3 Lead holes for wood screws loaded later- wood with G 0.6 (see Table 11.3.3A).ally shall be bored as follows: 11.1.6.4 Toe-nails shall be driven at an angle of ap- (a) For wood with G > 0.6 (see Table 11.3.3A), the proximately 30 with the member and started approxi- part of the lead hole receiving the shank shall mately 1/3 the length of the nail from the member end have about the same diameter as the shank, and (see Figure 11A). that receiving the threaded portion shall have about the same diameter as the screw at the Figure 11A Toe-Nail Connection

DOWEL-TYPE FASTENERS root of the thread (see Reference 8). (b) For G 0.6 (see Table 11.3.3A), the part of the lead hole receiving the shank shall be about 7/8 the diameter of the shank and that receiving the threaded portion shall be about 7/8 the diameter of the screw at the root of the thread (see Ref- erence 8). 11.1.5.4 The wood screw shall be inserted in itslead hole by turning with a screw driver or other tool,not by driving with a hammer. 11.1.5.5 No reduction to reference design values isanticipated if soap or other lubricant is used on the 11.1.6.5 The minimum length of nail or spike pene-wood screw or in the lead holes to facilitate insertion tration, pmin, including the length of the tapered tipand to prevent damage to the wood screw. where part of the penetration into the main member for single shear connections and the side members of dou- 11 11.1.5.6 The minimum length of wood screw pene-tration, pmin, including the length of the tapered tip ble shear connections shall be 6D.where part of the penetration into the main member forsingle shear connections and the side members for dou- Exception: The minimum length of penetration,ble shear connections shall be 6D. pmin, need not be 6D for symmetric double shear 11.1.5.7 Edge distances, end distances, and fastener connections where nails with diameter of 0.148spacings shall be sufficient to prevent splitting of the or smaller extend at least three diameters beyondwood. the side member and are clinched, and side members are at least 3/8" thick.11.1.6 Nails and Spikes 11.1.6.6 Edge distances, end distances, and fastener spacings shall be sufficient to prevent splitting of the 11.1.6.1 Installation requirements apply to common wood.steel wire nails and spikes, box nails, threaded hard-ened-steel nails, and post-frame ring shank nails meet- 11.1.7 Drift Bolts and Drift Pinsing requirements in ASTM F1667. Nail specificationsfor engineered construction shall include the minimumlengths and diameters for the nails and spikes to be 11.1.7.1 Lead holes shall be drilled 0" to 1/32"used. See Appendix Table L4 for standard common, smaller than the actual pin diameter. Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL74 DOWEL-TYPE FASTENERS

11.1.7.2 Additional penetration of pin into mem- 11.1.8 Other Dowel-Type

bers shall be provided in lieu of the washer, head, and Fastenersnut on a common bolt (see Reference 53 for additionalinformation). Where fastener type or installation requirements 11.1.7.3 Edge distances, end distances, and fastener vary from those specified in 11.1.3, 11.1.4, 11.1.5,spacings shall not be less than the requirements in Ta- 11.1.6, and 11.1.7, provisions of 11.2 and 11.3 shall bebles 11.5.1A through 11.5.1D. permitted to be used in the determination of reference withdrawal and lateral design values, respectively, pro- vided allowance is made to account for such variation (see 10.1.1.3). Edge distances, end distances, and spac- ings shall be sufficient to prevent splitting of the wood.

11.2 Reference Withdrawal Design Values

11.2.1 Lag Screws mined from Table 11.2B or Equation 11.2-2, within the range of specific gravities, G, and screw diameters, D, 11.2.1.1 The lag screw reference withdrawal design given in Table 11.2B. Reference withdrawal designvalues, W, in lbs/in. of thread penetration, for a single values, W, shall be multiplied by all applicable adjust-lag screw inserted in the side grain of a wood member, ment factors (see Table 10.3.1) to obtain adjusted with-with the lag screw axis perpendicular to the wood fi- drawal design values, W'.bers, shall be determined from Table 11.2A or Equation W = 2850 G2D (11.2-2)11.2-1, within the range of specific gravities, G, and lagscrew diameters, D, given in Table 11.2A. Reference 11.2.2.2 For calculation of the fastener referencewithdrawal design values, W, shall be multiplied by all withdrawal design value in pounds, the unit referenceapplicable adjustment factors (see Table 10.3.1) to ob- withdrawal design value in lbs/in. of thread penetrationtain adjusted withdrawal design values, W'. from 11.2.2.1 shall be multiplied by thelength of thread penetration, pt, into the wood member. W = 1800 G3/2D3/4 (11.2-1) 11.2.2.3 Wood screws shall not be loaded in with- 11.2.1.2 For calculation of the fastener reference drawal from end grain of wood.withdrawal design value in pounds, the unit reference 11.2.2.4 Where wood screws are loaded in with-withdrawal design value in lbs/in. of thread penetration drawal, the adjusted tensile strength of the wood screwfrom 11.2.1.1 shall be multiplied by thelength of thread at the net section (root diameter, Dr) shall not be ex-penetration, pt, into a wood member. ceeded (see 10.2.3 and Appendix Table L3). 11.2.1.3 Where lag screws are loaded in withdrawalfrom end grain, reference withdrawal design values, W, 11.2.3 Nails and Spikesshall be multiplied by the end grain factor, Ceg = 0.75. 11.2.3.1 The nail or spike reference withdrawal de- 11.2.1.4 Where lag screws are loaded in with- sign value, W, in lbs/in. of penetration, for a plaindrawal, the tensile strength of the lag screw at the net shank single nail or spike driven into the side grain of asection (root diameter, Dr) shall not be exceeded (see wood member, with the nail or spike axis perpendicular10.2.3 and Appendix Table L2). to the wood fibers, shall be determined from Table 11.2C or Equation 11.2-3, within the range of specific11.2.2 Wood Screws gravities, G, and nail or spike diameters, D, given in Table 11.2C. Reference withdrawal design values, W, 11.2.2.1 The wood screw reference withdrawal de- shall be multiplied by all applicable adjustment factorssign value, W, in lbs/in. of thread penetration, for a sin- (see Table 10.3.1) to obtain adjusted withdrawal designgle wood screw (cut thread or rolled thread) inserted in values, W'.the side grain of a wood member, with the wood screw W = 1380 G5/2 D (11.2-3)axis perpendicular to the wood fibers, shall be deter-

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11.2.3.2 For calculation of the fastener reference 11.2.3.4 For calculation of the fastener referencewithdrawal design value in pounds, the unit reference withdrawal design value in pounds, the unit referencewithdrawal design value in lbs/in. of fastener penetra- withdrawal design value in lbs/in. of ring shank pene-tion from 11.2.3.1 shall be multiplied by the length of tration from 11.2.3.3 shall be multiplied by the lengthfastener penetration, pt, into the wood member. of ring shank penetration, pt, into the wood member. 11.2.3.3 The reference withdrawal design value, in 11.2.3.5 Nails and spikes shall not be loaded inlbs/in. of penetration, for a single post-frame ring shank withdrawal from end grain of wood.nail driven in the side grain of the main member, withthe nail axis perpendicular to the wood fibers, shall be 11.2.4 Drift Bolts and Drift Pinsdetermined from Table 11.2D or Equation 11.2-4,within the range of specific gravities and nail diameters Reference withdrawal design values, W, for con-given in Table 11.2D. Reference withdrawal design nections using drift bolt and drift pin connections shallvalues, W, shall be multiplied by all applicable adjust- be determined in accordance with 10.1.1.3.ment factors (see Table 10.3.1) to obtain adjusted with-drawal design values, W'. W = 1800 G2 D (11.2-4)

11.3 Reference Lateral Design Values

11.3.1 Yield Limit Equations 11.3.2 Common Connection Reference lateral design values, Z, for single shear Conditionsand symmetric double shear connections using dowel-type fasteners shall be the minimum computed yield Reference lateral design values, Z, for connectionsmode value using equations in Tables 11.3.1A and with bolts (see Tables 11A through 11I), lag screws11.3.1B (see Figures 11B, 11C, and Appendix I) where: (see Tables 11J and 11K), wood screws (see Tables (a) the faces of the connected members are in contact; 11L and 11M), nails and spikes (see Tables 11N (b) the load acts perpendicular to the axis of the dowel; through 11R), and post-frame ring shank nails (see Ta- (c) edge distances, end distances, and spacing are not bles 11S and 11T), are calculated for common connec- less than the requirements in 11.5; and tion conditions in accordance with yield mode equa- (d) for lag screws, wood screws, and nails and spikes, tions in Tables 11.3.1A and 11.3.1B. Tabulated refer- the length of fastener penetration, p, into the main ence lateral design values, Z, shall be multiplied by ap- member of a single shear connection or the side plicable Table footnotes to determine an adjusted lat- member of a double shear connection is greater eral design value, Z'. than or equal to pmin (see 11.1). Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 79

1. Specific gravity, G, based on weight and volume when oven-dry. Different specific gravities, G, are possible for different grades of MSR and MEL lumber (see Table 4C, Footnote 2). Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL82 DOWEL-TYPE FASTENERS

Table 11.3.3B Dowel Bearing Figure 11B Single Shear Bolted

Strengths for Wood Connections Structural Panels

Dowel Bearing Specific1 Strength, Fe, in Wood Structural Gravity, pounds per square Panel G inch (psi) for D1/4" Plywood Figure 11C Double Shear Bolted Structural 1, Marine 0.50 4650 Connections Other Grades1 0.42 3350 Oriented Strand Board All Grades 0.50 4650 1. Use G = 0.42 when species of the plies is not known. When species of the plies is known, specific gravity listed for the actual species and the corresponding dowel bearing strength may be used, or the weighted average may be used for mixed species.

11.3.4 Dowel Bearing Strength at

an Angle to Grain 11.3.6 Dowel Bending Yield Where a member in a connection is loaded at an angleto grain, the dowel bearing strength, Fe, for the member Strengthshall be determined as follows (see Appendix J): 11.3.6.1 The reference lateral design values, Z, for Fe||Fe bolts, lag screws, wood screws, and nails are based on Fe (11.3-11) dowel bending yield strengths, Fyb, provided in Tables Fe|| sin Fe cos2 2

11A through 11T.

where: 11.3.6.2 Dowel bending yield strengths, Fyb, used in the determination of reference lateral design values, Z, = angle between the direction of load and the shall be based on yield strength derived using the direction of grain (longitudinal axis of methods provided in ASTM F 1575 or the tensile yield member) strength derived using the procedures of ASTM F 606.

11.3.5 Dowel Bearing Length 11.3.7 Dowel Diameter

11.3.5.1 Dowel bearing length in the side member(s) 11.3.7.1 Where used in Tables 11.3.1A or 11.3.1B,and main member, s and m, shall be determined based the fastener diameter shall be taken as D for unthreadedon the length of dowel bearing perpendicular to the appli- full-body diameter fasteners and Dr for reduced bodycation of load. diameter fasteners or threaded fasteners except as pro- 11.3.5.2 For lag screws, wood screws, nails, spikes, vided in 11.3.7.2.and similar dowel-type fasteners, the dowel bearing 11.3.7.2 For threaded full-body fasteners (see Ap-length, s or m, shall not exceed the length of fastener pendix L), D shall be permitted to be used in lieu of Drpenetration, p, into the wood member. Where p in- where the bearing length of the threads does not exceedcludes the length of a tapered tip, E, the dowel bearing of the full bearing length in the member holding thelength, s or m, shall not exceed p - E/2. threads. Alternatively, a more detailed analysis ac- a) For lag screws, E is permitted to be taken from counting for the moment and bearing resistance of the Appendix L, Table L2. threaded portion of the fastener shall be permitted (see b) For wood screws, nails, and spikes, E is permit- Appendix I). ted to be taken as 2D.

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11.3.8 Asymmetric Three Member 11E). The component of the load acting at 90 with the fastener axis shall not exceed the adjusted lateral designConnections, Double Shear value, Z', for a connection in which two members at 90 with the fastener axis have thicknesses ts = s and tm Reference lateral design values, Z, for asymmetric = m. Ample bearing area shall be provided to resist thethree member connections shall be the minimum com- load component acting parallel to the fastener axis.puted yield mode value for symmetric double shear 11.3.10.2 For toe-nailed connections, the minimumconnections using the smaller dowel bearing length in of ts or L/3 shall be used for s (see Figure 11A).the side member as s and the minimum dowel diame-ter, D, occurring in either of the connection shearplanes. 11.3.11 Drift Bolts and Drift Pins

Adjusted lateral design values, Z', for drift bolts and

11.3.9 Multiple Shear Connections drift pins driven in the side grain of wood shall not exceed 75% of the adjusted lateral design values for common For a connection with four or more members (see bolts of the same diameter and length in main member.Figure 11D), each shear plane shall be evaluated as asingle shear connection. The reference lateral designvalue, Z, for the connection shall be the lowest refer- Figure 11E Shear Area for Boltedence lateral design value for any single shear plane, Connectionsmultiplied by the number of shear planes.

DOWEL-TYPE FASTENERSFigure 11D Multiple Shear Bolted Connections

1111.3.10 Load at an Angle toFastener Axis

11.3.10.1 When the applied load in a single shear

(two member) connection is at an angle (other than 90)with the fastener axis, the fastener lengths in the twomembers shall be designated s and m (see Figure

11.4 Combined Lateral and Withdrawal Loads

11.4.1 Lag Screws and Wood (Wp)ZScrews Z (11.4-2) (Wp) cos Z sin

Where a lag screw or wood screw is subjected to where:

combined lateral and withdrawal loading, as when the = angle between the wood surface and thefastener is inserted perpendicular to the fiber and the direction of applied load, degreesload acts at an angle, , to the wood surface (see Figure11F), the adjusted design value, Z', shall be deter- p = length of fastener penetration into themined as follows (see Appendix J): main member, in.

(Wp)Z Figure 11F Combined Lateral and

p = length of thread penetration into the main

member, in.

11.4.2 Nails and Spikes

Where a nail or spike is subjected to combined lat-

eral and withdrawal loading, as when the nail or spikeis inserted perpendicular to the fiber and the load acts atan angle, , to the wood surface, the adjusted designvalue, Z', shall be determined as follows:

11.5 Adjustment of Reference Design Values

11.5.1 Geometry Factor, C (a) Where dowel-type fasteners are used and the actual end distance for parallel or perpendicular 11.5.1.1 For dowel-type fasteners where D < 1/4", to grain loading is greater than or equal to the minimum end distance (see Table 11.5.1A) forC = 1.0. C = 0.5, but less than the minimum end dis- 11.5.1.2 Where D 1/4" and the end distance or tance for C = 1.0, the geometry factor, C,spacing provided for dowel-type fasteners is less than shall be determined as follows:the minimum required for C = 1.0 for any condition in(a), (b), or (c), reference lateral design values, Z, shall C = actual end distancebe multiplied by the smallest applicable geometry fac- minimum end distance for C = 1.0tor, C, determined in (a), (b), or (c). The smallest ge-ometry factor for any fastener in a group shall apply toall fasteners in the group. For multiple shear connec-tions or for asymmetric three member connections, thesmallest geometry factor, C, for any shear plane shallapply to all fasteners in the connection.

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DOWEL-TYPE FASTENERS distance for distance forDirection of Loading C = 0.5 C = 1.0 with Table 11.5.1C and Table 11.5.1D and applicablePerpendicular to Grain 2D 4D requirements of 11.1. The perpendicular to grain dis-Parallel to Grain, tance between the outermost fasteners shall not exceedCompression: 5" (see Figure 11H) unless special detailing is provided(fastener bearing away to accommodate cross-grain shrinkage of the woodfrom member end) 2D 4D member. For structural glued laminated timber mem-Parallel to Grain, bers, the perpendicular to grain distance between theTension: outermost fasteners shall not exceed the limits in Table(fastener bearing to- 11.5.1F, unless special detailing is provided to accom-ward member end) modate cross-grain shrinkage of the member. for softwoods 3.5D 7D for hardwoods 2.5D 5D Table 11.5.1B Spacing Requirements (b) For loading at an angle to the fastener, where dowel-type fasteners are used, the minimum shear for Fasteners in a Row 11 area for C = 1.0 shall be equivalent to the shear area for a parallel member connection with mini- Spacing Direction of Minimum Minimum spacing mum end distance for C = 1.0 (see Table Loading spacing for C = 1.0 11.5.1A and Figure 11E). The minimum shear area for C = 0.5 shall be equivalent to the Parallel to Grain 3D 4D Perpendicular to 3D Required spacing for minimum shear area for C = 1.0. Where the ac- Grain attached members tual shear area is greater than or equal to the minimum shear area for C = 0.5, but less than 11.5.2 End Grain Factor, Ceg the minimum shear area for C = 1.0, the geome- 11.5.2.1 Where lag screws are loaded in with- try factor, C, shall be determined as follows: drawal from end grain, the reference withdrawal de- actual shear area sign values, W, shall be multiplied by the end grain C = minimum shear area for C = 1.0 factor, Ceg = 0.75. (c) Where the actual spacing between dowel-type 11.5.2.2 Where dowel-type fasteners are inserted fasteners in a row for parallel or perpendicular to in the end grain of the main member, with the fastener grain loading is greater than or equal to the mini- axis parallel to the wood fibers, reference lateral de- mum spacing (see Table 11.5.1B), but less than sign values, Z, shall be multiplied by the end grain the minimum spacing for C = 1.0, the geometry factor, Ceg = 0.67. Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL86 DOWEL-TYPE FASTENERS

11.6 Multiple Fasteners

Where a connection contains multiple fasteners, Local stresses in connections using multiple fas-fasteners shall be staggered symmetrically in members teners shall be evaluated in accordance with principlesloaded perpendicular to grain whenever possible (see of engineering mechanics (see 10.1.2).10.3.6.2 for special design provisions where bolts, lagscrews, or drift pins are staggered).

11.6.2 Fasteners Loaded at an

Angle to Grain

When a multiple fastener connection is loaded at

an angle to grain, the gravity axis of each membershall pass through the center of resistance of the groupof fasteners to insure uniform stress in the main mem-

DOWEL-TYPE FASTENERSber and a uniform distribution of load to all fasteners.

11

Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL 88 DOWEL-TYPE FASTENERSBOLTS Table 11A BOLTS: Reference Lateral Design Values, Z, for Single Shear (two member) Connections1,2 for sawn lumber or SCL with both members of identical specific gravity

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BOLTS DOWEL-TYPE FASTENERS This page left blank intentionally.

11

Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL 100 DOWEL-TYPE FASTENERSLAG SCREWS Table 11J LAG SCREWS: Reference Lateral Design Values, Z, for Single Shear (two member) Connections1,2,3,4 for sawn lumber or SCL with both members of identical specific gravity (tabulated lateral design values are calculated based on an assumed length of lag screw penetration, p, into the main member equal to 8D) Side Member

1. Tabulated lateral design values, Z, shall be multiplied by all applicable adjustment factors (see Table 10.3.1). 2. Tabulated lateral design values, Z, are for reduced body diameter lag screws (see Appendix Table L2) inserted in side grain with screw axis perpendicular to wood fibers; screw penetration, p, into the main member equal to 8D; screw bending yield strengths, Fyb,of 70,000 psi for D = 1/4", 60,000 psi for D = 5/16", and 45,000 psi for D 3/8". 3. Where the lag screw penetration, p, is less than 8D but not less than 4D, tabulated lateral design values, Z, shall be multiplied by p/8D or lateral design values shall be calculated using the provisions of 11.3 for the reduced penetration. 4. The length of lag screw penetration, p, not including the length of the tapered tip, E (see Appendix Table L2), of the lag screw into the main member shall not be less than 4D. See 11.1.4.6 for minimum length of penetration, pmin. Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 101

LAG SCREWSTable 11J LAG SCREWS: Reference Lateral Design Values (Z)(Cont.) for Single Shear (two member) Connections1,2,3,4 for sawn lumber or SCL with both members of identical specific gravity (tabulated lateral design values are calculated based on an assumed length of lag screw penetration, p, into the main member equal to 8D) G=0.36 Side Member

1. Tabulated lateral design values, Z, shall be multiplied by all applicable adjustment factors (see Table 10.3.1).2. Tabulated lateral design values, Z, are for reduced body diameter lag screws (see Appendix Table L2) inserted in side grain with screw axis perpendicular to wood fibers; screw penetration, p, into the main member equal to 8D; screw bending yield strengths, Fyb,of 70,000 psi for D = 1/4", 60,000 psi for D = 5/16", and 45,000 psi for D 3/8".3. Where the lag screw penetration, p, is less than 8D but not less than 4D, tabulated lateral design values, Z, shall be multiplied by p/8D or lateral design values shall be calculated using the provisions of 11.3 for the reduced penetration.4. The length of lag screw penetration, p, not including the length of the tapered tip, E (see Appendix Table L2), of the lag screw into the main member shall not be less than 4D. See 11.1.4.6 for minimum length of penetration, pmin. Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUINCIL 102 DOWEL-TYPE FASTENERSLAG SCREWS Table 11K LAG SCREWS: Reference Lateral Design Values, Z, for Single Shear (two member) Connections1,2,3,4 for sawn lumber or SCL with ASTM A653, Grade 33 steel side plate (for ts<1/4") or ASTM A 36 steel side plate (for ts=1/4") (tabulated lateral design values are calculated based on an assumed length of lag screw penetration, p, into the main member equal to 8D)

Eastern Softwoods Spruce-Pine-Fir(S) Douglas Fir-Larch

Douglas Fir-Larch

Northern Species Western Cedars Western Woods Spruce-Pine-Fir Douglas Fir(S) Southern Pine Side Member

1. Tabulated lateral design values, Z, shall be multiplied by all applicable adjustment factors (see Table 10.3.1). 2. Tabulated lateral design values, Z, are for reduced body diameter lag screws (see Appendix Table L2) inserted in side grain with screw axis perpendicular to wood fibers; screw penetration, p, into the main member equal to 8D; dowel bearing strengths, Fe, of 61,850 psi for ASTM A653, Grade 33 steel and 87,000 psi for ASTM A36 steel and screw bending yield strengths, Fyb, of 70,000 psi for D = 1/4", 60,000 psi for D = 5/16", and 45,000 psi for D 3/8". 3. Where the lag screw penetration, p, is less than 8D but not less than 4D, tabulated lateral design values, Z, shall be multiplied by p/8D or lateral design values shall be calculated using the provisions of 11.3 for the reduced penetration. 4. The length of lag screw penetration, p, not including the length of the tapered tip, E (see Appendix Table L2), of the lag screw into the main member shall not be less than 4D. See 11.1.4.6 for minimum length of penetration, pmin.

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WOOD SCREWSTable 11L WOOD SCREWS: Reference Lateral Design Values, Z, for Single Shear (two member) Connections1,2,3 for sawn lumber or SCL with both members of identical specific gravity (tabulated lateral design values are calculated based on an assumed length of wood screw penetration, p, into the main member equal to 10D)

Douglas Fir-Larch(N)

Eastern Softwoods Spruce-Pine-Fir(S) Douglas Fir-Larch

Northern Species Western Cedars Western Woods Spruce-Pine-Fir Douglas Fir(S) Southern Pine Side Member

NAILSTable 11N COMMON, BOX, or SINKER STEEL WIRE NAILS: Reference Lateral Design Values, Z, for Single Shear (two member) Connections1,2,3 for sawn lumber or SCL with both members of identical specific gravity (tabulated lateral design values are calculated based on an assumed length of nail penetration, p, into the main member equal to 10D)

Eastern Softwoods Common Wire Nail

Spruce-Pine-Fir(S) Douglas Fir-Larch

Douglas Fir-Larch

Northern Species Western Cedars Western Woods Spruce-Pine-Fir Douglas Fir(S) Southern Pine Nail Diameter Side Member

NAILSTable 11R COMMON, BOX, or SINKER STEEL WIRE NAILS: Reference Lateral Design Values, Z, for Single Shear (two member) Connections1,2,3 with wood structural panel side members with an effective G=0.42 (tabulated lateral design values are calculated based on an assumed nail penetration, p, into the main member equal to 10D) Common Wire Nail

Eastern Softwoods Spruce-Pine-Fir(S) Douglas Fir-Larch

Douglas Fir-Larch

Northern Species Western Cedars Western Woods Spruce-Pine-Fir Douglas Fir(S) Southern Pine Nail Diameter Side Member

A connector unit shall be defined as one of the fol-

lowing: (a) One split ring with its bolt or lag screw in sin- gle shear (see Figure 12A). 12.1.3 Quality of Split Ring and (b) Two shear plates used back to back in the con- tact faces of a wood-to-wood connection with Shear Plate Connectors their bolt or lag screw in single shear (see Fig- 12.1.3.1 Design provisions and reference design ures 12B and 12C). values herein apply to split ring and shear plate connec- (c) One shear plate with its bolt or lag screw in sin- tors of the following quality: gle shear used in conjunction with a steel strap (a) Split rings manufactured from SAE 1010 hot or shape in a wood-to-metal connection (see rolled carbon steel (Reference 37). Each ring Figures 12B and 12C). shall form a closed true circle with the principal axis of the cross section of the ring metal paral- lel to the geometric axis of the ring. The ringFigure 12A Split Ring Connector shall fit snugly in the precut groove. This shall be accomplished with a ring, the metal section of which is beveled from the central portion toward the edges to a thickness less than at midsection, or by any other method which will accomplish equivalent performance. It shall be cut through in one place in its circumference to form a tongue and slot (see Figure 12A). (b) Shear plate connectors: (1) 2-5/8" Pressed Steel TypePressed steel shear plates manufactured from SAE 1010 (Reference 37) hot rolled carbon steel.Figure 12B Pressed Steel Shear Each plate shall be a true circle with a Plate Connector flange around the edge, extending at right angles to the face of the plate and extend- ing from one face only, the plate portion having a central bolt hole, with an integral hub concentric to the hole or without an in- tegral hub, and two small perforations on opposite sides of the hole and midway from the center and circumference (see Figure 12B). (2) 4" Malleable Iron TypeMalleable iron shear plates manufactured according to Grade 32510 of ASTM Standard A47 (Ref- erence 11). Each casting shall consist of a Copyright American Wood Council. Downloaded/printed pursuant to License Agreement. No reproduction or transfer authorized. AMERICAN WOOD COUNCIL NATIONAL DESIGN SPECIFICATION FOR WOOD CONSTRUCTION 115

perforated round plate with a flange around differ slightly in shape and cross section, cutter heads the edge extending at right angles to the shall be designed to produce daps and grooves con- face of the plate and projecting from one forming accurately to the dimensions and shape of the face only, the plate portion having a central particular split ring or shear plate connectors used. bolt hole with an integral hub extending 12.1.4.2 Where lag screws are used in place of from the same face as the flange (see Fig- bolts, the hole for the unthreaded shank shall be the ure 12C). same diameter as the shank. The diameter of the hole 12.1.3.2 Dimensions for typical split ring and shear for the threaded portion of the lag screw shall be ap-plate connectors are provided in Appendix K. Dimen- proximately 70% of the shank diameter, or as specifiedsional tolerances of split ring and shear plate connectors in 11.1.4.2.shall not be greater than those conforming to standard 12.1.4.3 In installation of split ring or shear platepractices for the machine operations involved in manu- connectors and bolts or lag screws, a nut shall be placedfacturing the connectors. on each bolt, and washers, not smaller than the size 12.1.3.3 Bolts used with split ring and shear plate specified in Appendix K, shall be placed between theconnectors shall conform to 11.1.3. The bolt shall have outside wood member and the bolt or lag screw headan unreduced nominal or shank (body) diameter in ac- and between the outside wood member and nut. Wherecordance with ANSI/ASME Standard B18.2.1 (Refer- an outside member of a shear plate connection is a steelence 7). strap or shape, the washer is not required, except where 12.1.3.4 Where lag screws are used in place of a longer bolt or lag screw is used, in which case, the

SPLIT RING AND SHEAR PLATE CONNECTORS

bolts, the lag screws shall conform to 11.1.3 and the washer prevents the metal plate or shape from bearingshank of the lag screw shall have the same diameter as on the threaded portion of the bolt or lag screw.the bolt specified for the split ring or shear plate con- 12.1.4.4 Reference design values for split ring andnector (see Tables 12.2A and 12.2B). The lag screw shear plate connectors are based on the assumption thatshall have an unreduced nominal or shank (body) di- the faces of the members are brought into contact whenameter and threads in accordance with ANSI/ASME the connector units are installed, and allow for seasonalStandard B18.2.1 (see Reference 7). variations after the wood has reached the moisture con- tent normal to the conditions of service. Where split12.1.4 Fabrication and Assembly ring or shear plate connectors are installed in wood which is not seasoned to the moisture content normal to 12.1.4.1 The grooves, daps, and bolt holes specified the conditions of service, the connections shall be tight-in Appendix K shall be accurately cut or bored and ened by turning down the nuts periodically until mois-shall be oriented in contacting faces. Since split ring ture equilibrium is reached.and shear plate connectors from different manufacturers